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Aspirin is very soluble in ether. If 0.372g of aspirin are dissolved in 2.97g of diethyl ether, the vapor pressure of the ether lowers from 0.631 to 0.601 atm at 23^oC. What is the molecular weight of the aspirin?

In order to be able to find the vapour pressure of the solution the mole fraction of both the ether and the aspirin.

1 mole ether = 60g and 1 mole aspirin = ?g

Therefore the moles of each component are:

This means that the mole fraction of ether can be found:

This would make the vapour pressure of the solution as:

Where x would be 150.1g

States of Matter

There are three different states of matter: solids, liquids and gases.

These three states of matter behave differently in space:

• Solids have got a both a fixed volume and fixed shape. It can increase and decrease slightly in size with changes in the temperature.
• Liquids have got a fixed volume but they would take the shape of the container. A change in temperature would have a change in volume.
• Gases have got no fixed volume nor shape and a change in temperature would have a very big change in volume.

Different states of matter would have different energies and thus it can be noted that each particle would be able to react differently to different conditions. This can be explained by the kinetic theory. The kinetic theory states that:

• All matter is made up of particles.
• The particles are moving all the time.
• Heavier particles move slower then lighter particles.

This can then be used to analyse the interactions found in each of the states of matter.

• Solids would have their particles very close together which would be held by very strong forces making it very difficult for individual particles to be able to roam freely, but these particles can vibrate.
• Liquids would still have forces between separate particles, but they would be much weaker, allowing individual particles to roam around in a random way.
• In gases no forces are found between separate particles allowing the particles to roam around freely and at very high velocities.

Diffusion

Diffusion is the movement of a substance from an area of high concentration to an area of low concentration

As discussed in the kinetic theory, particles in liquids and gases are constantly on the move. This would result in the migration of particles from one place to another resulting in the process of diffusion which can be observed as migration of chemicals from a high concentration to a place of a lower concentration. This process of diffusion can be observed as:

Bromine liquid in the bottom glass cylinder is evaporating, producing an orange gas. When allowed into contact with the cylinder filled with air (top), the two tend to try to equalise by molecules moving from an area of higher concentration to one of lower – upward for the bromine and downward for the air.

Rates of Diffusion

The rate of diffusion is related to the mass of the molecules. The bigger the mass, the slower the rate of diffusion. An experiment to show the difference in the rate of diffusion is the following:

The two gases will diffuse at different rates, with the lightest particle moving faster than the heaviest particle. Since HCl is heavier than NH₃, the white cloud formed when the two interact will be closer to the hydrogen chloride.

Brownian motion

Particles in both liquids and gases (collectively called fluids) move randomly. This is called Brownian motion. They do this because they are bombarded by the other moving particles in the fluid. Larger particles can be moved by light, fast-moving molecules.

Brownian motion is named after the botanist Robert Brown, who first observed this in 1827. He used a microscope to look at pollen grains moving randomly in water. At this point, he could not explain why this occurred.

Some examples of Brownian Motion are pollen grains on the surface of water and smoke in air.

Changes of states

Matter can easily interchange between different states of matter, with the most important changes being between solids and liquids and liquids and gases, although it must be noted that solids can sublime to form a gas without forming liquid as an intermediate

On heating the energy of the particles would increase and once enough energy is given to the particles they would be able to overcome the strong forces between the particles to melt and produce a liquid. This would be the melting temperature. If the temperature is increased then the particles would obtain even more energy would be taken by the particles and until the energy is high enough for each particles to escape the effects of the other particles to form a gas. This temperature would be the boiling point

When the temperature is reduced the gases would go back to being a liquid while liquids would form a solid, with the processes being known as condensation and solidification respectively.

In some special cases solids can form gases without the formation of liquids, with such an example being Carbon Dioxide. The temperature at which this process occurs is called the sublimation point while the reverse process os called deposition.

Melting and Boiling Point Graph

Each substance has its own unique melting and boiling point. For water the melting/freezing point is 0 ^oC and the boiling/condensation point is 100 ^oC.

In fact, for a pure substance the melting and boiling points are always constant, and therefore if you want to check for the purity of water you can check its melting and boiling points. If they are 0 and 100^oC respectively then it will be pure water.

 

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Question 1

Balance the following equations in acidic conditions:

1. As₂O₃+ NO₃^– à H₃AsO₄ + N₂O₃
2. MnO₄^– + S₂O₃^2– à Mn²⁺+ SO₄^2–
3. H₂O₂+ Cr₂O₇²¯ àCr³⁺ + O₂ + H₂O
4. IO₃^– + SO₂ à I₂ + SO₄^2–
5. Cr₂O₇^2– + Mn²⁺à Cr²⁺ + MnO₄^–
6. H₃PO₂+ Cr₂O₇^2– à H₃PO₄ + Cr³⁺
7. As + ClO₃^– à H₃AsO₃ + HClO

 

Question 2

Balance the following equations in basic conditions:

1. MnO₄^– + SO₃^2– à MnO₂+ SO₄^2-
2. HPO₃^2– + N₂H₄à H₂PO₂^– + N₂
3. Cr + CrO₄^2– à Cr(OH)₃
4. CrO₄²¯ + S₂O₄²¯ à Cr(OH)₃ + SO₄^2–
5. CN^– + MnO₄^– à CNO^– + MnO₂
6. MnO₂+ O₂ à MnO₄^– + H₂O
7. MnO₄^– + C₂O₄^2– à CO₂+ MnO₂

Question 3

0.2640 g of sodium oxalate is dissolved in a flask and requires 30.74 mL of potassium permanganate (from a buret) to titrate it and cause it to turn pink (the end point).

The equation for this reaction is:

5Na₂C₂O₄ + 2KMnO₄ + 8H₂SO₄ à 2MnSO₄ + K₂SO₄ + 5Na₂SO₄ + 10CO₂ + 8H₂O

1. How many moles of sodium oxalate are present in the flask?
2. How many moles of potassium permanganate have been titrated into the flask to reach the end point?
3. What is the molarity of the potassium permanganate?

Question 4

Potassium dichromate is used to titrate a sample containing an unknown percentage of iron. The sample is dissolved in H₃PO₄/H₂SO₄ mixture to reduce all of the iron to Fe²⁺ ions. The solution is then titrated with 0.01625 M K₂Cr₂O₇, producing Fe³⁺ and Cr³⁺ ions in acidic solution. The titration requires 32.26 mL of K₂Cr₂O₇ for 1.2765 g of the sample.

1. Balance the net ionic equation using the half-reaction method.
2. Determine the percent iron in the sample.
3. Is the sample ferrous iodate, ferrous phosphate, or ferrous acetate?

Question 5

The quantity of antimony in a sample can be determined by an oxidation-reduction titration with an oxidizing agent. A 9.62 g sample of stibnite, an ore of antimony, is dissolved in hot, concentrated HCl and passed over a reducing agent so that all the antimony is in the form Sb³⁺. The Sb³⁺ is completely oxidized by 43.70 mL of a 0.1250 M solution of KBrO₃. Calculate the amount of antimony in the sample and its percentage in the ore.

Question 6

The amount of I₃^– in a solution can be determined by titration with a solution containing a known concentration of S₂O₃²– (thiosulfate ion). The determination is based on the balanced equation:

I₃^– + 2S₂O₃^2– à 3I^– + S₄O₆^2–

Given that it requires 36.40 mL of 0.3300 M Na₂S₂O₃ to titrate the I₃^– in a 15.00 mL sample, calculate the molarity of I₃^– in the solution.

 

Question 7

A solution of I₃^–(aq) can be standardized by using it to titrate As₄O₆(aq). The titration of 0.1021 g of As₄O₆(s) dissolved in 30.00 mL of water requires 36.55 mL of I₃^–. Calculate the molarity of the I₃^– solution. The unbalanced equation is

As₄O₆ + I₃^– —> As₄O₁₀ + I^–

 

Question 1

Some pure magnesium carbonate was added to 145. mL of 1.00 M HCl. When the reaction had finished, the solution was acidic. 25.0 mL of 0.500 M Na₂CO₃ solution was required to neutralize the excess acid. What mass of magnesium carbonate was originally used?

Question 2

A 25.00 mL sample of HCl was added to a 0.1996 g sample of CaCO₃. All the CaCO₃ reacted, leaving some excess HCl.

CaCO₃ + 2HCl à CaCl₂ + H₂O + CO₂

The excess HCl required 48.96 mL of a 0.01044 M barium hydroxide solution for complete neutralization.

2HCl + Ba(OH)₂ à BaCl₂ + 2H₂O

What was the molarity of the original HCl?

Question 3

A chemist measured the amount of CaCO₃ present in an antacid tablet. A tablet weighing 0.743 g was dissolved in 25.0 mL of 0.500 M HCl, and boiled to remove the CO₂ gas. The chemical reaction is this:

CaCO₃ + 2HCl  à CaCl₂ + CO₂ + H₂O

The amount of HCl added was more than enough to react with all of the calcium carbonate present in the tablet

The excess HCl was back-titrated with 0.1500 M NaOH, requiring 16.07 mL of the NaOH solution to reach the endpoint.

What is the mass percent of CaCO₃ in the antacid tablet?

 

Question 4

 

A 0.3017 g sample of a diprotic acid (molar mass = 126.07 g/mol) was dissolved in water and titrated with a 37.26 mL sample of sodium hydroxide. A 24.05 mL sample of this sodium hydroxide was then used to react with 0.2506 g of an unknown acid, which has been determined to be monoprotic. What is the molar mass of the unknown acid?

 

 

Question 5

4.65 g of Co(OH)₂ is dissolved in 500.0 mL of solution. 3.64 g of an unknown acid is dissolved in 250.0 mL of solution. 18.115 mL of the base is used to titrate 25.0 mL of the acid to its endpoint. Calculate the molar mass of the acid and identify it.

 

Question 1

A solution of sodium hydroxide contained 0.250 mol dm^-3. Using phenolphthalein indicator, titration of 25.0 cm³ of this solution required 22.5 cm³ of a hydrochloric acid solution for complete neutralisation.

1. write the equation for the titration reaction.
2. what apparatus would you use to measure out (i) the sodium hydroxide solution? (ii) the hydrochloric acid solution?
3. what would you rinse your apparatus out with before doing the titration ?
4. what is the indicator colour change at the end-point?
5. calculate the moles of sodium hydroxide neutralised.
6. calculate the moles of hydrochloric acid neutralised.
7. calculate the concentration of the hydrochloric acid in mol/dm³(molarity).

Question 2

A solution made from pure barium hydroxide contained 2.74 g in exactly 100 cm³ of water. Using phenolphthalein indicator, titration of 20.0 cm³ of this solution required 18.7 cm³ of a hydrochloric acid solution for complete neutralisation. [atomic masses: Ba = 137, O = 16, H = 1)

1. write the equation for the titration reaction.
2. calculate the molarity of the barium hydroxide solution.
3. calculate the moles of barium hydroxide neutralised.
4. calculate the moles of hydrochloric acid neutralised.
5. calculate the molarity of the hydrochloric acid.

 

Question 3

25 cm³ of a solution of 0.1 moldm^-3 NaOH reacts with 50 cm³ of a solution of hydrochloric acid. What is the molarity of the acid?

 

Question 4

25.0 cm³ of a 0.10 moldm^-3 solution of sodium hydroxide was titrated against a solution of hydrochloric acid of unknown concentration. 27.3 cm³ of the acid was required. What was the concentration of the acid?

 

Question 5

 

10 cm³ of a solution of NaCl react with 15 cm³ of  a 0.02 moldm^-3 solution of AgNO₃. What is the concentration of the NaCl solution in gdm^-3?

 

 

Question 6

 

25 cm³ of a 0.1 moldm^-3 solution of an acid H_xA reacts with 75 cm³ of a 0.1 moldm^-3 solution of NaOH. What is the value of x?

Equation: H_xA + xNaOH à + Na_xA + xH₂O

 

Question 7

 

A solution of hydrochloric acid of volume 25.0 cm³ was pipetted onto a piece of marble which is calcium carbonate. When all action had ceased, 1.30g of the marble had dissolved. Find the concentration of the acid

Equation: CaCO₃ + 2HCl à CaCl₂ + CO₂ + H₂O

 

Question 8

What volume of 0.1 moldm^-3 hydrochloric acid would be required to dissolve 2.3 g of calcium carbonate?

Equation: CaCO₃(s) + 2HCl(aq) à CaCl₂(aq) + CO₂(g) + H₂O(l)

 

Question 9

 

2.05 g of the carbonate of an unknown alkali metal (X₂CO₃) required 8.9 cm³ of 2.0 moldm^-3 hydrochloric acid to completely dissolve it. What was the relative atomic mass of the metal and which metal was it?

Equation: X₂CO₃(s) + 2HCl(aq) à 2XCl(aq) + CO₂(g) + H₂O(l)

Question 10

3.2 g of hydrated sodium carbonate, Na₂CO₃.xH₂O, was dissolved in water and the resulting solution was titrated against 1.0 moldm^-3 hydrochloric acid. 22.4 cm³ of the acid was required. What is the value of x?

 

Question 1

Calculate the volume occupied by one mole of a gas at 25 ^oC and 100 kPa.

 

Question 2

 

Calculate the pressure of a gas given that 0.2 moles of the gas occupy 10 dm³ at 20 ^oC.

 

Question 3

Calculate the temperature of a gas if 0.5 moles occupy 1.2 dm³ at a pressure of 200 kPa.

 

Question 4

 

Calculate the mass of a sample of carbon dioxide which occupies 20 dm³ at 27 ^oC and 100 kPa.

 

Question 5

 

Calculate the relative molecular mass of a gas if a 500 cm³ sample at 20 ^oC and 1 atm has a mass of 0.66 g.

 

Question 6

 

At 25 ^oC and 100 kPa a gas occupies a volume of 20 dm³. Calculate the new temperature of the gas if

1. the volume is decreased to 10 dm³ at constant pressure.
2. the pressure is decreased to 50 kPa at constant volume.

 

Question 7

10.0 g of calcium nitrate is heated at 100 kPa and a temperature of 300 ^oC, at which temperature it fully decomposes. Calculate

1. the volume of nitrogen dioxide evolved
2. the volume of oxygen evolved
3. the total volume of gas evolved

Equation: 2Ca(NO₃)₂(s) à 2CaO(s) + 4NO₂(g) + O₂(g)

 

 

Question 8

Calculate the colume of oxygen produced at 298K and 100 kPa by the decomposition of 30 cm³ of 0.1 mol dm^_3 H₂O₂.

Equation: 2H₂O₂(aq) à 2H₂O(l) + O₂(g)

 

Question 9

What mass of magnesium, and what volume of 2.0 moldm-3 hydrochloric acid, will be required to produce 100 cm3 of hydrogen gas at 298 K and 100 kPa?

Equation: Mg(s) + 2HCl(aq) à MgCl₂(aq) + H₂(g)

 

Question 10

0.52 g of sodium was added to 100 cm³ of water. Calculate:

1. The volume of hydrogen evolved at 298 K and 100 kPa
2. The concentration of the sodium hydroxide solution produced, assuming the volume of water does not change.

Equation: 2Na(s) + 2H₂O(l) à 2NaOH(aq) + H₂(g)

 

Question 11

A balloon has a mass of 0.5 g when completely deflated. When it is filled with an unknown gas, the mass increases to 1.7 g. You notice on the canister of the unknown gas that it occupies a volume of 0.4478 L at a temperature of 50 °C. You note the temperature in the room is 25 °C. Identify the gas.

 

Question 12

A gas consisting of only carbon and hydrogen has an empirical formula of CH₂. The gas has a density of 1.65 g/L at 27.0 °C and 97858 Pa. Determine the molar mass and molecular formula of the gas.

 

Question 13

Container A holds N₂ gas with a mass of 56.2 g and is 4.4 times the volume of container B which holds argon (Ar) gas at the exact same temperature and pressure. What is the mass of the Ar (in g) within container B?

 

 

 

Question 1

Calculate the number of moles of H₂SO₄ in 50 cm³ of a 0.50 moldm^-3 solution.

 

Question 2

Calculate the number of moles of FeSO₄ in 25 cm³ of a 0.2 moldm^-3 solution.

 

Question 3

Calculate the mass of KMnO₄ in 25 cm³ of a 0.02 moldm^-3 solution.

 

 

Question 4

Calculate the mass of Pb(NO₃)₂ in 30 cm³ of a 0.1 moldm^-3 solution.

 

Question 5

What is the molarity of 1.06g of H₂SO₄ in 250 cm³ of solution?

 

Question 6

What is the molarity of 15.0 g of CuSO₄.5H₂O in 250 cm³ of solution?

 

Question 7

What volume of a 0.833 moldm^-3 solution of H₂O₂ will be required to make 250 cm³ of a 0.100 moldm^-3 solution?

 

Question 8

What volume of a 0.50 moldm^-3 solution of HCl will be required to make 100 cm³ of a 0.050M solution?

 

Question 9

How many moles of NaCl are there in 25 cm³ of a 50 gdm^-3 solution?

 

Question 10

What is the concentration of each type of ion in solution after 23.69 mL of 3.611 M NaOH is added to 29.10 mL of 0.8921 M H₂SO₄? Assume that the final volume is the sum of the original volumes.

Question 11

Given 8.00 g of HBr calculate the volume (mL) of a 48.0% (weight/weight) solution. (MW HBr: 80.9119 g/mol, density: 1.49 g/mL). Then, calculate the molarity.

 

Question 12

A solution is made by dissolving 0.100 mol of NaCl in 4.90 mol of water. What is the mass % of NaCl?

 

Question 13

You need to make an 80.0 g mixture of ethanol and water containing equal molar amounts of both, what mass of each substance would be required?

Question 1

What is the empirical formula of a compound containing 60.0% sulfur and 40.0% oxygen by mass?

Question 2

A compound is found to contain 23.3% magnesium, 30.7% sulfur, and 46.0% oxygen. What is the empirical formula of this compound?

Question 3

What is the empirical formula for a compound containing 38.8% carbon, 16.2% hydrogen, and 45.1% nitrogen?

Question 4

A sample of an oxide of nitrogen is found to contain 30.4% nitrogen. What is its empirical formula?

Question 5

A sample of an oxide of arsenic is found to contain 75.74% arsenic. What is its empirical formula?

Question 6

What is the empirical formula for a compound containing 26.57% potassium, 35.36% chromium, and 38.07% oxygen?

Question 7

A compound with an empirical formula of C2OH4 and a molar mass of 88. What is the molecular formula of this compound?

Question 8

A compound with an empirical formula of C4H4O and a molar mass of 136. What is the molecular formula of this compound?

Question 9

A compound that is 9.4% C, 14.9% F, 62.7% Br, and 6.3% Oxygen has a molar mass of 237.8. What is the molecular formula of this compound?

 

Question 10

A carbohydrate on analysis gave the following composition: carbon = 40.0%; hydrogen = 6.71%, and oxygen made up the rest. Calculate the molecular formula of this organic compound which has a molecular mass of 181.

Question 11

Nicotine is mainly responsible for the addictive nature of cigarettes. A typical cigarette contains 12.33 mg C, 1.45 mg H, & 2.87 mg N. If the molar mass of nicotine is 162 g/mol, what is the molecular formula of nicotine?

Question 12

An unknown compound was found to have a percent composition as follows: 47.0 % potassium, 14.5 % carbon, and 38.5 % oxygen. What is its empirical formula? If the true molar mass of the compound is 166.22 g/mol, what is its molecular formula?

Question 13

NutraSweet is 57.14% C, 6.16% H, 9.52% N, and 27.18% O. Calculate the empirical formula of NutraSweet and find the molecular formula. (The molar mass of NutraSweet is 294.30 g/mol)

Question 14

What’s the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29% Oxygen? If the molar mass is 110 g/mol, what is the molecular formula?

Question 15

Caffeine has the following percent composition: 49.47% C, 5.201% H, 28.84% N, and 16.48% O If the molecular mass of caffeine is 194.2 amu, what is it’s molecular formula?

 

Question 16

The combustion of 3.42 g of a compound is known to contain only nitrogen and hydrogen gave 9.82 g of NO₂ and 3.85 g of water. Determine the empirical formula of this compound.

Question 17

A 2.52 g sample of a compound containing carbon, hydrogen, nitrogen, oxygen, and sulfur was burned in excess oxygen gas to yield 4.36 grams of CO₂ and 0.892 grams of H₂O as the only carbon and hydrogen products respectively. Another sample of the same compound of mass 4.14 g yielded 2.60 g of SO₃ as the only sulfur containing product. A third sample of mass 5.66 g was burned under different conditions to yield 2.80 g of HNO₃ as the only nitrogen containing product. Determine the empirical formula of the compound.

 

Question 18

A compound with a known molecular weight (146.99 g/mol) that contains only C, H, and Cl was studied by combustion analysis. When a 0.367 g sample was combusted, 0.659 g of CO₂ and 0.0892 g of H₂O formed. What are the empirical and molecular formulas?

 

Question 19

A 6.20-g sample of an unknown compound containing only C, H, and O combusts in an oxygen rich environment. When the products have cooled to 20.0 °C at 1 bar, there are 8.09 L of CO₂ and 3.99 mL of H₂O. The density of water at 20.0 °C is 0.998 g/mL.

Question 1

Given the chemical equation

Na_(s) + H₂O_(ℓ) → NaOH_(aq) + H_2(g)

1. a)  Balance the equation.
2. b)  How many molecules of H₂are produced when 332 atoms of Na react?

 

Question 2

Given the chemical equation

S_(s) + O_2(g) → SO_3(g)

1. a)  Balance the equation.
2. b)  How many molecules of O₂are needed when 38 atoms of S react?

 

Question 3

For the balanced chemical equation

6 H⁺_(aq) + 2 MnO₄⁻_(aq) + 5 H₂O_2(ℓ) → 2 Mn²⁺_(aq) + 5 O_2(g) + 8 H₂O_(ℓ)

how many molecules of H2O are produced when 75 molecules of H2O2 react?

 

Question 4

For the balanced chemical reaction

2 C₆H_6(ℓ) + 15 O_2(g) → 12 CO_2(g) + 6 H₂O_(ℓ)

how many molecules of CO₂ are produced when 56 molecules of C6H6 react?

 

Question 5

Given the balanced chemical equation

Fe₂O_3(s) + 3SO_3(g) → Fe₂(SO₄)₃

how many molecules of Fe₂(SO₄)₃ are produced if 321 atoms of S are reacted?

 

Question 6

For the balanced chemical equation

CuO_(s) + H_2(g) → Cu_(s)  + H₂O_(ℓ)

how many moles of CuS are formed if 2g of H₂ react?

 

Question 7

For the balanced chemical equation

Fe₂O_3(s) + 3 SO_3(g) → Fe₂(SO₄)₃

suppose we need to make 145,000 molecules of Fe₂(SO₄)₃. How many molecules of SO₃ do we need?

 

Question 8

One way to make sulfur hexafluoride is to react thioformaldehyde, CH₂S, with elemental fluorine:

CH₂S + 6 F₂ → CF₄ + 2 HF + SF₆

If 45,750 molecules of SF₆ are needed, how many molecules of F₂ are required?

 

 

 

Question 1

4. How many atoms are present in 4.55 mol of Fe?
5. How many atoms are present in 0.0665 mol of K?
6. How many molecules are present in 2.509 mol of H2_S?
7. How many molecules are present in 0.336 mol of acetylene (C₂H₂)?
8. How many moles are present in 3.55 × 1024 Pb atoms?
9. How many moles are present in 2.09 × 1022 Ti atoms?
10. How many moles are present in 1.00 × 1023 PF₃molecules?
11. How many moles are present in 5.52 × 1025 penicillin molecules?

 

Question 2

Determine the molar mass of each substance.

1. Si
2. SiH₄
3. K₂O
4. Cl₂
5. SeCl₂
6. Ca(C₂H₃O₂)₂

 

Question 3

What is the mass of 4.44 mol of Rb?

What is the mass of 0.311 mol of Xe?

What is the mass of 12.34 mol of Fe₂(SO₄)₃?

What is the mass of 0.0656 mol of PbCl₂?

 

Question 4

How many moles are present in 45.6 g of CO?

How many moles are present in 0.00339 g of LiF?

How many moles are present in 1.223 g of SF₆?

How many moles are present in 48.8 g of BaCO₃?

 

Question 5 

How many moles are present in 54.8 mL of mercury if the density of mercury is 13.6 g/mL?

How many moles are present in 56.83 mL of O₂ if the density of O₂ is 0.00133 g/mL?