Salts

Question 1

how can a soluble salt be prepared with an insoluble reactant? (3)

Answer 1

by reacting an acid with:

a metal
a metal oxide
a carbonate

Question 2

why do chemists avoid reacting metals and acids?

-what is the alternative?

Answer 2

• reaction between metals and acids produces flammable hydrogen,
• reacting a metal oxide or a metal carbonate with an acid.

Question 3

what are salt names comprised of?

-what are they?

Answer 3

two parts

• first is the metal, metal oxide or metal carbonate
• second is the acid

Question 4

what do different acids produce? (3)

-in reference to hydrochloric acid, nitric acid and sulfuric acid

Answer 4

• hydrochloric acid produces chloride salts
• nitric acid produces nitrate salts
• sulfuric acid produces sulfate salts

Question 5

Method to making a soluble salt from an acid and an insoluble reactant: (5)

Answer 5

• Add some dilute hydrochloric acid to a beaker.
• Add powdered insoluble reactant to some acid in a beaker, one spatula at a time, stirring to mix. The mixture will effervesce.
• Continue adding powder until some unreacted powder is left over - it is in excess.
• Filter the mixture in the beaker to remove the excess powder.
• Allow the water in the solution to evaporate (by heating and/or leaving for a few days) to obtain pure dry crystals of the salt.

Question 6

Notes on each step of making a salt: (3)

Answer 6

• To make sure all of the acid has reacted, add the excess of the solid reactant.
• Filtering removes the unreacted insoluble reactant from the salt solution.
• As the acid is all used up and the insoluble reactant has been removed, this only leaves the salt and water. Therefore evaporating the water leaves the pure salt.

Question 7

how can a soluble salt be prepared by reacting an acid with a soluble reactant?

Answer 7

-the soluble reactant is usually a dilute solution of an alkali

Question 8

what is a substance’s solubility?

Answer 8

a measure of the maximum mass that will dissolve in a given volume of a solvent, at a particular temperature

Question 9

discuss the solubility of a substance using terms such as ‘high and low solubilities’ (2)

Answer 9

• substances that are very soluble have high solubilities.

- substances that are insoluble or sparingly soluble (almost none dissolves) have low solubilities.

Question 10

common soluble ionic compounds: (2)

Answer 10

• all common sodium, potassium and ammonium salts

- all nitrates

Question 11

soluble and insoluble chlorides: (3)

Answer 11

soluble:
- most common chlorides

insoluble:

• silver chloride
• lead chloride

Question 12

soluble and insoluble sulfates: (4)

Answer 12

soluble:
- most common sulfates

insoluble:

• lead sulfate
• barium sulfate
• calcium sulfate

Question 13

soluble and insoluble carbonate: (4)

Answer 13

soluble:

• Sodium carbonate
• potassium carbonate
• ammonium carbonate

insoluble:
-most common carbonates

Question 14

soluble and insoluble hydroxides: (4)

Answer 14

soluble:

• sodium hydroxide
• potassium hydroxide
• ammonium hydroxide

insoluble:
-most common hydroxides

Question 15

what is a precipitate?

-and what is the reaction that produces them called?

Answer 15

an insoluble product that forms when two solutions are mixed and react together

• precipitation reaction.

Question 16

what is crucial for a precipitation reaction formula?

-why?

Answer 16

state symbols

-without them, we would not be able to distinguish between the precipitate and the other products from the reaction

Question 17

how can the formation of a precipitate be predicted? (3)

Answer 17

by using solubility rules

• if the products meet the ‘soluble’ rules in the left hand column, no precipitate will form
• if at least one product meets the ‘insoluble’ rule in the right hand column, a precipitate will form

Question 18

how could you determine suitable solutions to form precipitates?

Answer 18

All nitrates and all sodium salts are soluble. a given precipitate XY can be produced by mixing together solutions of:

X nitrate
sodium Y

where ‘X’ is the intended first part of the compound and ‘Y’ is the second

Question 19

outline method for making a pure, dry sample of an insoluble salt: (4)

Answer 19

1- Mix together two suitable solutions (see above).
2- Use filtration to separate the precipitate as a residue from the solution.
3- Wash the precipitate th distilled water while it is in the filter funnel.
4- Leave the washed precipitate aside or in a warm oven to dry.

Question 20

reasons for each step for making a pure, dry sample of an insoluble salt. (2)

Answer 20

• filtration separates insoluble substances from liquids and solutions.
• precipitate is insoluble in water, so any remaining contaminating solution can be removed by washing it with distilled water.