C3.4 Acids, ions, and metals

Question 1

What can a flame test be used for?

Answer 1

To detect the presence of a metal ion in a compound

Question 2

How do you complete a flame test?

Answer 2

Dip a clean loop in the sample solution
Hold the flame test in the bunsen burner flame
Observe the colour of the flame

Question 3

How do you test for positive ions ( cations )

eg SODIUM bromide

Answer 3

• Dissolve a small amount in water
• Add sodium hydroxide solution
• Identify the colour of the precipitate formed

If there is a WHITE precipitate, add MORE sodium hydroxide, If the precipitate does not dissolve, DO A FLAME TEST

Question 4

What colour precipitate does iron II form

Answer 4

Green

Question 5

What cation forms a red/brown precipitate?

Answer 5

Iron III

Question 6

How can you identify copper?

Answer 6

Blue precipitate

Question 7

What colour flames do Lithium, Magnesium, and Sodium produce?

Answer 7

Lithium = Red
Magnesium = No colour
Sodium = Yellow

Question 8

Which cations would lilac or brick red flames indicate?

Answer 8

Lilac = potassium

Brick red = calcium

Question 9

How do you test for negative ions (anions)?

Answer 9

• Dissolve in water
• Add Hydrochloric acid

If A gas is given off = CARBONATE
If no gas is given off ….

-Add hydrochloric acid + Barium chloride
If a white precipitate is formed = SULPHATE
OR
-Add nitric acid and silver nitrate to fresh solution
identify the colour precipitate formed

Question 10

What ion is present when a white precipitate is formed?

Answer 10

CHLORIDE

Question 11

How do you identify a BROMIDE ion

Answer 11

Forms a CREAM precipitate with nitric acid and silver nitrate

Question 12

What ion is present when a YELLOW precipitate is formed?

Answer 12

IODIDE

Question 13

How are titrations used to identify the acidity of a solution?

Answer 13

Titrations can be used to determine the volume of acid and alkali needed to react together to produce a neutral solution

Question 14

25 cm3 of dilute hydrochloric acid is neutralised by 20 cm3 of 0.5 mol/dm3 sodium hydroxide. What is the concentration of the hydrochloric acid?

Answer 14

-Convert volumes to dm3
-Determine the number of moles of sodium hydroxide
(moles of NaOH = concentration × volume)
-Work out the number of moles of acid using the balanced equation
- Calculate the concentration of the acid
(concentration of HCl = number of moles ÷ volume)

Ans = 0.4mol/dm3