Chapter 8 Acids and Alkalis

Question 1

What is the pH scale?

Answer 1

It is a way of measuring the acidity or alkalinity of a solution

Question 2

What is an indicator?

Answer 2

A substance that changes color based on the pH9

Question 3

What is a dilute acid?

Answer 3

are acids that have been mixed with
a lot of water before putting them out for use.
Their bottles are labelled with a hazard symbol

Question 4

Name the three indicators

Answer 4

Methyl orange
Phenophthalein
Litmus

Question 5

What are the colours the methyl orange indicator turns into in alkaline and acidic solutions?

Answer 5

Yellow in alkaline
Red in acids

Question 6

What are the colours the Phenolphthalein indicator turns into in alkaline and acidic solutions?

Answer 6

Pink in alkaline
Colorless in acidic

Question 7

What are the colours the Litmus indicator turns into in alkaline and acidic solutions?

Answer 7

Blue alkaline
Red Acidic

Question 8

Name the three common acids and their formula.

Answer 8

Hydrochloric acid - HCL
Nitric acid - HNO3
Sulfuric acid - H2SO4

Question 9

Formula for concentration.

Answer 9

Amount Dissolved
Concentration=—————————————–
Volume of solution

Question 10

1 dm cubed is how many cm cubed?

Answer 10

1000

Question 11

How is the pH of a solution measured?

Answer 11

By the concentration of hydrogen ions in the solution.

Question 12

What are the two types of acids?

Answer 12

Strong acids and Weak acids

Question 13

What determines if an acid is strong?

Answer 13

their molecules dissociate (break up) completely into ions when dissolved in water and produce a high concentration of hydrogen ions

Question 14

What are the two factors that affect the chemical properties of the acid?

Answer 14

its concentration - concentrated/dilute
If its weak or strong

Question 15

What are Bases?

Answer 15

Bases are substances that neutralize acids to form a salt and water ONLY.

Question 16

What are the four type of state symbols?

Answer 16

Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)

Question 17

What is the Titration apparatus?

Answer 17

Safety filler
pipette
Flask
Beaker
Burrette
Stand
Tap

Question 18

How can you make a soluble salt using titration?

Answer 18

Fill the burette with acid.
 Record the initial volume of acid in the burette.
 Measure alkali into a conical flask using a pipette and pipette filler.
 Add a few drops of indicator in the conical flask.
 Add acid from the burette by opening the tap.
 Continue to add acid until colour change occurs (end-point reached)
 Record the final volume of acid in the burette.
 Calculate the titre (by subtracting
final-initial volume)
 Repeat the titration until concordant titres are obtained (values that agree
within ± 0.20 cm3 ).
 Calculate the average volume(titre) of acid needed to neutralise the
alkali.
 Use the burette to add the average volume of acid without the indicator.
 Add salt solution to an evaporating basin
 Heat to evaporate some of the water and allow the solution to cool down
so that crystals form.
 Filter excess liquid
 Leave the crystals to dry in a warm place/warm oven

Question 19

How can you make sure you get accurate
results during titrations?

Answer 19

• Add the solution from the burette drop by
  drop near the end-point- Stop the titration when the indicator
  changes colour permanently- Repeat the titration until we get two
  concordant results, two titres that agree
  within 0.20 cm3 and find an average titre
  value

Question 20

What is the test for hydrogen gas?

Answer 20

To test for hydrogen, place a lighted splint
in the tube of gas. If a squeaky pop is
heard, the gas is hydrogen.

Question 21

What is the test for carbon dioxide gas?

Answer 21

Bubble the Gas through limewater, if the limewater turns from colorless to milky/cloudy

Question 22

What is a precipitation reaction?

Answer 22

When a reaction causes a insoluble precipitate to form

Question 23

How can you prepare an insoluble salt
in the lab?

Answer 23

1. Mix the solutions in a beaker to form a precipitate
2. Filter the mixture
3. Rinse the beaker with a little distilled water and
   pour this through the funnel.
4. Pour a little distilled water over the precipitate in
   the funnel.
5. Carefully remove the filter paper containing the
   precipitate and dry it in a warm oven/leave it to dry
   in the air/dry on filter paper or tissue

Question 24

How to write an ionic equation:

Answer 24

1. write down the full equation for the reaction and
   balance it
2. for dissolved ionic substances (aq), write the ions
   separately, keeping the state symbol next to each
   ion.
3. for all liquids, gases and solids (whether ionic or
   not), rewrite the full formula.
4. cross out all the ‘spectator’ ions (the ions that do not
   take part in a reaction)
5. Write the ‘net’ ionic equation