Acids and alkalis Flashcards
The pH scale shows how __ a substance is. It can be measured using a __ which gives a numerical value.
acidic
ph meter
The pH scale ranges from 0 (very __) through 7 (___) to 14 (very__ ).
acidic
neutral
alkaline
pH can be also be measured using an indicator and comparing the __ with a comparison chart.
colour
Do you think pure water is acidic, alkaline or neutral?
Pure water is neutral.
However, water comes from different sources, like tap water or river water. These water samples have other substances dissolved in them. They might show up as slightly acidic or slightly alkaline because of this.
What is used to find the pH of the substances?
A universal indicator.
It gives different colours at different pH values in a rainbow pattern from 0 (red) to 14 (purple). The indicator comes in solution or paper forms.
The pH scale is a number scale from __ to __ It tells us how acidic or alkaline an aqueous solution is. The pH scale is used to classify solutions as __, __ or __ .
0
14
acidic
alkaline
neutral
Neutral solutions are exactly pH __
7
Acidic solutions have pH values less than __ The closer to pH __ , the more acidic a solution is.
7
0
Alkaline solutions have pH values more than __. The closer to pH __ , the more alkaline a solution is.
7
14
Everyday substances are not__. This makes it difficult to give them a pH value. One type of soap might have a pH of 8, but another have a pH of 9.
pure
The term aqueous solutiondescribes a solution that’s made of__ . pH can only be measured in __-based solutions.
water
water
Therefore, we can measure a substance’s pH by __ it in water.
dissolving
Copper sulfate is a solid in the form of blue crystals. When copper sulfate is dissolved in pure water, we can measure the __ of the solution.
pH
The pH of Copper sulfate is approximately 6 which shows that copper sulfate solution is slightly __ .
acidic
A substance has a pH of 8. How would it be classified ?
The pH is above 7, so the substance would be classified an alkali.
There are 2 methods for testing for pH:
- Using a pH meter
- Using an indicator
An indicator is a substance which will change __ depending on the pH of the solution it is mixed with.
colour
Some indicators are __ , meaning we can add drops of the indicator to the solution being tested. Other indicators are strips of __ , and we can dip these into the solution.
liquids
paper
__ is an example of an indicator. It turns red in solutions that are acidic and it is blue in alkaline solutions.
Litmus
Universal indicator is a special indicator because it turns into a different __ at many different pH values.
colour
An indicator is added to a solution. It turns green. What is the pH of the solution?
Show answer
It’s not possible to know. There are lots of different indicators and they give different colours at different pH values. Without the exact name of the indicator, it is not possible to know what the colour means.
Unlike litmus, __ can show us how strongly acidic or alkaline a solution is, not just that the solution is acidic or alkaline.
universal indicator
A few drops of universal indicator are added to water. Then some lemon juice is squeezed in. What colour change would happen?
Lemon juice is acidic (approximately 2 on the pH scale), so the water would change colour from green to yellow/orange.
Lots of highly coloured __ and __ can be used to make indicators just by mashing them in hot water.
vegetables
flowers
An acid and alkali will__ each other and produce a salt and water.
neutralise
What is a neutralisation reaction?
A chemical reaction happens if you mix together an acid and a base.
The name of the __ produced can be worked out from the names of the acid and the alkali.
salt
What are the names of the substances formed in a neutralisation reaction?
Salt and water.
Neutralisation is an __ reaction, so the reaction mixture warms up during the reaction.
exothermic
Salts have scientific names. For example, the scientific name of table salt is __ .
sodium chloride
Names of salts can be worked out from the names of the __ and the __ that react to make them.
acid
alkali
There are two parts to a salt name:
The first word is a __ , taken from the alkali.
The second word ends in ~ide or ~ate, taken from the __ .
metal
acid
table salt – or sodium chloride - is produced when hydrochloric acid reacts with the alkali sodium hydroxide. The word __ is taken from the alkali, and the word __ from the acid.
sodium
chloride
There are three acids that are commonly used to make salrs. These are __ , and .
hydrochloric acid
nitric acid
sulfuric acid
A salt made from hydrochloric acid will end in __
chloride
A salt made from nitric acid will end in __
nitrate
A salt made from sulfuric acid will end in __
sulfate
Can you work out the name of the salt made from potassium hydroxide and hydrochloric acid?
Potassium chloride.
Working backwards, the names of the acid and alkali reacting can be predicted from the name of the salt.
For example, the salt lithium nitrate would have been made from __ and __ .
lithium hydroxide
nitric acid
The second word in the name of a salt comes from which of the reactants?
The second word of the name is taken from the name of the acid.
For example:
Hydrochloric acid → chloride
Nitric acid → nitrate
Sulfuric acid → sulfate
Neutralisation reactions can be described using chemical equations like a word equation. This uses the scientific names for the __ and __ placed on the reactant side of the equation. The scientific name for the __ goes on the product side, together with water.
acid
alkali
salt
Acids always have ___ in them.
hydrogen (H)
hydrochloric acid has the formula __
HCl
sulfuric acid has the formula __
H₂SO₄
nitric acid has the formula __
HNO₃.
Alkalis have the __ in their formula
hydroxide group OH
sodium hydroxide has the formula __
NaOH
The H from the acid combines with the OH from the alkali to make the __ . The other elements are used in making the formula of the __ .
water (H₂O)
salt
Acids react with most __ .
metals
When an acid reacts with a metal, the products are a __ and.
salt
hydrogen
This is the general word equation for the reaction of an acid and a metal:
metal + acid → salt + hydrogen
What would the pH of an acidic solution be?
Below 7.
A solution with a pH value which is less than 7 is acidic. The acids which react with metals usually have quite a low pH, of either 3 or less.
What are the names of the products made in the reaction between an acid and a metal?
Salt and hydrogen.
Acids react with some metals to produce a __ and __ gas.
salt
hydrogen
The abbreviation M.A.S.H. stands for:
Metal + acid → salt + hydrogen
When a metal is put in acid, it gets__ and __ as it gets used up in the chemical reaction.
smaller
smaller
When a metal is put in acid, bubbles of gas can be seen. The bubbles produced in the reaction are __ gas.
hydrogen
How can you prove the existence of hydrogen gas?
Using a burning splint because hydrogen is flammable..
When the burning splint is put into the test tube containing hydrogen gas, a small explosion occurs, making a squeaky pop sound.
What is seen when a metal reacts with an acid?
- Bubbles being produced
- The metal getting smaller
If we put the metals in order of their reactivity, from the most reactive down to the least reactive, we get a list called the __
reactivity series.
Gold reacts with acids to produce lots of bubbles.
True of false?
False!
Gold is not a reactive metal, meaning it does not corrode and is easily malleable over a flame, making it a good element for jewellery making.
The name of the salt formed from the reaction of a metal and acid can be worked out using the names of the __ and the __ .
metal
acid
acid
The scientific name of table salt is __. It is produced when __ reacts with __ .
sodium chloride
sodium
hydrochloric acid
Naming the salt from the reaction of a metal and an acid
- The first word is the name of the __
- The second word of the name is taken from the name of the
metal
acid
Magnesium and Nitric acid from __
Magnesium nitrate
Calcium and Hydrochloric acid from __
Calcium chloride
Zinc and Sulfuric acid from __
Zinc sulfate
word equation for magnesium and sulfuric acid
magnesium + sulfuric acid → magnesium sulfate + hydrogen
symbol equation for magnesium and sulfuric acid
Mg + H₂SO₄ → MgSO₄ + H₂
What is the name of the salt formed when iron reacts with sulfuric acid?
Iron sulfate.
The word and symbol equation for this reaction is:
Iron + sulfuric acid → iron sulfate + hydrogen
Fe + H₂SO₄ → FeSO₄ + H₂
what is an acid?
Corrosive substance which has a pH lower than 7. Acidity is caused by a high concentration of hydrogen ions.
what is an alkali?
A base which is soluble in water.
what is a base?
A substance that reacts with an acid to neutralise it and produce a salt.
what does corrosive mean?
Able to damage metal, stonework, clothes and skin. Strong acids and alkalis are corrosive.
what does neutralise mean?
To be made neutral by removing any acidic or alkaline nature.
Bases are usually: (3)
- metal oxides, such as copper oxide
- metal hydroxides, such as sodium hydroxide, or
- metal carbonates, such as calcium carbonate
Household cleaning products contain strong __
bases
Alkalis feel __ when they get on your skin
soapy
Just like concentrated acids, concentrated alkalis are ___ . They can attack metals and destroy skin if spilled
corrosive
