SC8 - Acids and Alkalis

Question 1

SC8a - What are alkalis a source of in solution?

Answer 1

OH- ions

Question 2

SC8a - What are the tests for carbon dioxide?

Answer 2

bubble the gas through limewater (calcium hydroxide solution); the limewater turns milky if CO2 is present.

Question 3

SC8a - What are the tests for hydrogen?

Answer 3

1. Burning wooden splinter is extinguished in hydrogen 2. Hydrogen burns with a pale blue fame producing a pop sound Squeaky Pop Test!

Question 4

SC8a - What colour is litmus in acidic solutions?

What colour is litmus in alkaline solution?

Answer 4

Red in acidic solutions

Blue when in alkaline solutions

Question 5

SC8a - What colour is methyl orange in acidic solution?

What colour is methyl orange in alkaline solution?

Answer 5

Red in acid

Yellow in alkaline

Question 6

SC8a - What colour is phenolphthalein in acidic solution?

What colour is phenolphthalein in alkaline solutions?

Answer 6

Colourless in acidic solutions

Pink in alkaline solution

Question 7

SC8a -What are acids a source of in solution?

Answer 7

H+ ions

Question 8

SC8b - How can you test the acidity of a solution?

Answer 8

Using universal indicator

Question 9

SC8b - How do you calculate concentration?

Answer 9

Concentration = amount (g)/volume (dm3)

Question 10

SC8b - How do you make a solution more concentrated?

Answer 10

Add more solute / Evaporate some water

Question 11

SC8b - How do you make a solution more dilute?

Answer 11

Add more water

Question 12

SC8b - What is a base?

Answer 12

A substance that reacts with an acid to make salt and water only

Question 13

SC8b - What is the chemical formula for hydrochloric acid?

Answer 13

HCl

Question 14

SC8b - What is the chemical formula for nitric acid?

Answer 14

HNO3

Question 15

SC8b - What is the chemical formula for sulfuric acid?

Answer 15

H2SO4 (aq)

Question 16

SC8b - Why do strong acids have a lower pH than weak acids?

Answer 16

Strong acids completely dissociate in H+ ions when in solution; whereas weak acids only partially dissociate into H+ ions. This means there is a higher concentration of H+ ions in the strong acids, therefore they have a lower pH

Question 17

SC8b -If the pH increases by 1; what happens to the concentration of hydrogen ions?

Answer 17

Decreased by a factor of 10

Question 18

SC8c - How can soluble salt be made from acid and alkalis?

Answer 18

In an neutralisation reaction between an acid and an alkali. The end point of this reaction is found using an indicator. The salt can obtained from the solution by evaporation

Question 19

SC8c - How do you convert cm into dm?

Answer 19

divide by 1000

Question 20

SC8c - Represent a neutralisation reaction in an equation

Answer 20

H+ + OH- —> H20

Question 21

SC8c CP - Describe how to prepare a soluble salt from an acid and base

Answer 21

1. Add excess base to ensure all acid reacts
2. Warm in water bath
3. Filter out the unreactive solid
4. Evaporate the water in water bath so the salt can be concentrated
5. Leave to cool and for remaining water to evaporate so crystallisation can take place

Question 22

SC8c CP - Why; when making copper sulfate; do we add the metal oxide in excess?

Answer 22

To ensure all the acid reacts

Question 23

SC8c- How can soluble salt be made from acids and metals?

Answer 23

In a reaction; an acid and a metal makes a salt and a hydrogen.

Question 24

SC8d - What are spectator ions?

Answer 24

Ions that do not change during the reaction

Question 25

SC8e - Describe titration experiment

Answer 25

1. Use a pipette to transfer 25cm3 of alkali NAOH into a conical flask 2. Add 5 drop of indicator eg methyl orange which is yellow in alkali or phenothplaein which is pink In alkali into conical flask 3. Make sure there is a white tile under the conical flask so color change is apparent 4. Now add a known amount of acid into the burette 5. Open the tap of burette slowly and allow the drops of acid to go into the conical flask whilst swirling it and do this until the solution is neutralised so phenothphlain will turn coloruless in neutral 6. After reaching the endpoint, record the volume of acid dispensed as indicated on the burette. Calculate the amount of acid used by subtracting the initial volume from the final volume observed. 7. Repeat this experiment and find average to then find the conc of acid

Question 26

SC8e - How do we make a pure dry salt from titration?

Answer 26

- Carry out a titration - Note the exact volume of acid needed to neutralise the alkali - Use the burette to add the correct volume of acid without the indicator this time (as alrdy know correct amount of acid to put in)- Evaporate water from solution formed, crystallisation

Question 27

SC8e - What is a buret?

Answer 27

A long; narrow; graduated tube used to add titrate

Question 28

SC8e - What is a stopcock?

Answer 28

A small tap that is used to control the flow of the titrate during titration

Question 29

SC8f - hat metals react steadily with dilute acids?

Answer 29

Metals in the middle of the reactivity series such as magnesium or zinc (because metals in the top react violently and metals in the end might not even react)

Question 30

SC8f - State the general equation for the reaction between an acid and a metal carbonate

Answer 30

metal carbonate + acid --\> salt + water + carbon dioxide

Question 31

SC8f - What is a reduction reaction?

Answer 31

gain of electrons

Question 32

SC8f - What is an oxidation reaction?

Answer 32

loss of electrons

Question 33

SC8f - What is effervescence?

Answer 33

rapid escape of a gas from a liquid

Question 34

SC8f - What metals do not react with dilute acids?

Answer 34

Copper; Silver

Question 35

SC8f - What metals react explosively with dilute acids?

Answer 35

Potassium; Sodium

Question 36

SC8g - Describe the steps required to produce a pure; dry sample of an insoluble salt from two soluble salts

Answer 36

-1. Mix the 2 soluble salts together in water solution form 2. The insoluble salt will form as a precipitate 3. Wash the precipitate in the beaker to remove the soluble impurities and pour this through a filter paper to filter out the water 4. Capture and remove the precipitate from filter paper and dry in warm oven

Question 37

SC8g - How can soluble salt be made from ammonia solution?

Answer 37

By reacting ammonia solution with an acid; ammonium salt and water are produced.

Question 38

SC8g - How can we check whether a precipitate will form?

Answer 38

To determine if a precipitate will form in a reaction, check the solubility of the potential products using solubility rules. If any of the reaction products is an insoluble salt, it will form a precipitate. If all possible products are soluble, they remain dissolved, and no precipitate will be seen

Question 39

SC8g - What are ammonium salts used for?

Answer 39

fertilisers

Question 40

SC8g - What carbonates are soluble?

Answer 40

sodium; potassium; ammonium

Question 41

SC8g - What chlorides are insoluble?

Answer 41

Silver and lead

Question 42

SC8g - What happens when two solutions containing soluble salts react together?

Answer 42

The metals from the salts swap

Question 43

SC8g - What hydroxides are soluble?

Answer 43

sodium; potassium; ammonium

Question 44

SC8g - What is a precipitation reaction?

Answer 44

When two soluble substances react together to make a product which is insoluble (the precipitate)

Question 45

SC8g - What substances are generally insoluble?

Answer 45

Most carbonates most hydroxides

Question 46

SC8g - What substances are generally soluble?

Answer 46

all common sodium,pottassium and ammonium salts all nitrates most chlorides most sulfates

Question 47

SC8g - What sulfates are insoluble?

Answer 47

Lead; barium and calcium