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End of chapter exercises

Give one word for each of the following descriptions:

1. the change in phase of water from a gas to a liquid

2. a charged atom

3. a term used to describe the mineral content of water

4. a gas that forms sulphuric acid when it reacts with water

a) Condensation

b) Ion

c) Water hardness

d) Sulphur trioxide ($S{O}_{3}$)

Match the information in column A with the information in column B by writing only the letter (A to I) next to the question number (1 to 7)

Table 1
 Column A Column B 1. A polar molecule A. $H 2 SO 4$ 2. Molecular solution B. $CaCO 3$ 3. Mineral that increases water hardness C. $NaOH$ 4. Substance that increases the hydrogen ion concentration D. salt water 5. A strong electrolyte E. calcium 6. A white precipitate F. carbon dioxide 7. A non-conductor of electricity G. potassium nitrate H. sugar water I. $O 2$

1) B

2) H

3) E

4) A

5) C

6) B

7)  I

Explain the difference between a weak electrolyte and a strong electrolyte. Give a generalised equation for each.

A strong electrolyte ionises completely in water, while a weak electrolyte only ionises partially. In a strong electrolyte all the substance is found as ions, while in a weak electrolyte some of the molecules do not dissociate.

A strong electrolyte may be represented by:

$AB\left(s,l,g\right)\to {A}^{+}\left(aq\right)+{B}^{-}\left(aq\right)$

A weak electrolyte may be represented by:

$AB\left(s,l,g\right)\to AB\left(aq\right)⇌{A}^{+}\left(aq\right)+{B}^{-}\left(aq\right)$

What factors affect the conductivity of water? How do each of these affect the conductivity?

The type of substance: whether a substance is a strong electrolyte, a weak electrolyte or a non electrolyte affects the concentration of ions in solution.

The concentration of ions in solution: The more ions there are in solution, the greater the conductivity will be.

The temperature: Higher temperatures increase solubility and so increase the concentration of ions in solution.

For each of the following substances state whether they are molecular or ionic. If they are ionic, give a balanced reaction for the dissociation in water.

1. methane ($CH 4$)

2. potassium bromide

3. carbon dioxide

4. hexane ($C 6 H 14$)

5. lithium fluoride ($LiF$)

6. magnesium chloride

1. Molecular
2. Ionic  $\text{KBr}+{\text{H}}_{2}\text{O}\to {\text{K}}^{+}+{\text{Br}}^{-}+{\text{H}}_{2}\text{O}$
3. Molecular
4. Molecular
5. Ionic  ${\text{MgCl}}_{2}+{\text{H}}_{2}\text{O}\to {\text{Mg}}^{2+}+2{\text{Cl}}^{-}+{\text{H}}_{2}\text{O}$

Three test tubes (X, Y and Z) each contain a solution of an unknown potassium salt. The following observations were made during a practical investigation to identify the solutions in the test tubes:

A: A white precipitate formed when silver nitrate ($AgNO 3$) was added to test tube Z.

B: A white precipitate formed in test tubes X and Y when barium chloride ($BaCl 2$) was added.

C: The precipitate in test tube X dissolved in hydrochloric acid ($HCl$) and a gas was released.

D: The precipitate in test tube Y was insoluble in hydrochloric acid.

1. Use the above information to identify the solutions in each of the test tubes X, Y and Z.

2. Write a chemical equation for the reaction that took place in test tube X before hydrochloric acid was added.

(DoE Exemplar Paper 2 2007)

a) X: Carbonate solution

Y: Sulphate solution

Z: Chloride solution

b) $CO32-+B{a}^{2}++C{l}^{-}\to BaC{O}_{3}+C{l}^{-}$