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