Acids and Bases Flashcards Preview

IGCSE Chemistry- Part 2 > Acids and Bases > Flashcards

Flashcards in Acids and Bases Deck (24):
1

what is the use of the indicator litmus to distinguish between acid and alkaline solutions?

- in acid, turns red
- in neutral, turns purple
- in alkali, turns blue

2

what is the use of the indicator phenolphthalein?

- in acid, turns colourless
- in neutral, turns colourless
- in alkali, turns pink

3

what is the use of the indicator methyl orange?

- in acid, turns red
- in neutral, turns orange
- in alkali, turns yellow

4

what are solutions with a pH less than 7?

acidic

5

what are solutions with a pH greater than 7?

alkali

6

what are solutions with a pH of 7?

neutral

7

what forms does universal indicator come in?

- liquid solution in ethanol
- paper that has been soaked in the indicator solution

8

what is universal indicator?

It is a mixture of a variety of other indicators and can be used to measure the approximate pH of a solution

9

what is universal indicator used for?

When universal indicator is added to a solution it changes to a colour that shows the pH of the solution (using the ph scale)

10

what is an acid?

a substance that dissolves in water to produce hydrogen ions (H+)

11

what is an alkali?

a substance that dissolved in water to produce hydroxide ions (OH-)

12

describe the reactions of hydrochloric acid and sulfuric acid with metal hydroxides

metal hydroxides, such as sodium hydroxide, usually dissolve in water to form clear, colourless solutions. When an acid reacts with a metal hydroxide, the only products formed are a salt plus water. acid+metal hydroxide= a salt+water. Usually observe these things:
- there is a temperature rise
- the pH of the reaction mixture changes

13

what are the general rules for predicting the solubility of salts in water?

- all common sodium, potassium and ammonium salts are soluble
- all nitrates are soluble
- common chlorides are soluble (except silver chloride)
- common sulphates are soluble (except those of barium and calcium)
- common carbonates are insoluble (except those of sodium, potassium and ammonium)

14

what is the meaning of soluble?

able to be dissolved

15

describe an experiment to prepare soluble salts from acids (acid+insoluble base)

- put some dilute acid into a beaker and heat it using bunsen burner, do not let boil
- add the insoluble base, a little bit at a time, to the warm dilute acid and stir until the base is in excess
- filter the mixture into an evaporating basin to remove the excess base
- leave the filtrate in a warm place so the water evaporates and crystals form
- remove the crystals and dry them on filter paper

16

describe an experiment to prepare soluble salts from acids (acid+soluble base (alkali))

 Put an aqueous solution of the alkali into a conical flask and add a suitable
indicator (e.g. litmus or methyl orange)
 Add dilute acid from a burette until the indicator just changes colour.
 Add powdered charcoal and shake the mixture to remove the colour of the
indicator.
 Filter to remove the charcoal and then obtain crystals from the filtrate in the usual
manner.

17

what is a precipitate?

an insoluble solid that is made by a chemical reaction that takes place in an aqueous solution

18

what is a precipitate reaction?

a reaction that produces a precipitate

19

describe a precipitate reaction?

- to make an insoluble salt, mix together two separate aqueous solutions
- one solution must contain the required positive ion and the other the required negative ion
- the precipitate is then removed by filtration, washed with a little distilled water and left to dry in a warm place

20

describe an experiment to carry out acid-alkali titrations?

1. Using a pipette, put 25.0cm3 of an alkali solution into a conical flask.
2. Add a few drops of an indicator, such as methyl orange.
3. Put the acid in a pipette and note the initial reading.
4. Add the acid to the alkali until the indicator just changes colour.
5. Note the final reading of acid in the burette.
6. Subtract the initial reading to obtain the volume of acid added. This is the volume
required to neutralise the 25.0cm3 of the alkali.

21

what is a titration?

a method of finding out exactly the volume of one solution that is required to react with a given volume of another solution

22

what are titrations commonly used for?

to find out the volume of acid required to react exactly with a given volume of alkali

23

describe the reactions of hydrochloric acid and sulfuric acid with metal oxides

some metal oxides, such as sodium oxide, dissolve in water to form clear, colourless solutions. Many of them are not soluble in water, but they will react with acids. Copper oxide is like this. When an acid reacts with a metal oxide, the only products formed are a salt plus water. acid+metal oxide= a salt+water. Usually observe these things:
- there is a temperature rise
- the pH of the reaction mixture changes

24

describe the reactions of hydrochloric acid and sulfuric acid with metal carbonates

although sodium carbonate can dissolve in water, most metal carbonates are not soluble. Calcium carbonate (chalk, limestone and marble) is like this. When an acid reacts with a metal carbonate, the products formed are a salt plus water, but carbon dioxide is also formed. acid+metal carbonate= a salt+water+carbon dioxide
You usually observe bubbles of gas being given off during the reaction. You can show that the gas is co2 by bubbling it through limewater: this turns cloudy white when it reacts with water