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Thank you for visiting this blog. We hope you have learnt more about acids, alkalis and pH values. :)))

Testing for acids and alkalis

Below are some of the ways whereby you can test for acids and alkalis.

TESTING FOR ACIDS
1. blue litmus paper - blue litmus paper turns red in acid
2. universal indicator - acids will have a pH value of less than 7
3. pH meter - acids will have a pH value of less than 7
4. carbonates - acids react with carbonates to produce carbon dioxide gas, salt and water
5. alkalis - acids react with alkalis to produce salt and water
6. metals - acids react with metals to produce hydrogen gas and salt

TESTING FOR ALKALIS
1. red litmus paper - red litmus paper turns blue in alkali
2. universal indicator - alkalis will have a pH value of more than 7
3. pH meter - alkalis will have a pH value of more than 7
4. acids - acids react with alkalis to produce salt and water
5. ammonium salt - alkalis react with ammonium salts to produce ammonia gas, salt and water

More on Acids and Alkalis

Acids and alkalis are 2 different types of solutions. Below shows some of the properties of acids and alkalis.

ACIDS
- neutralise alkalis
- turn litmus paper from blue to red
- produces hydrogen gas when mixed with certain metals
- produces carbon dioxide gas when mixed with carbonates
- are good electrical conductors
- have a sour taste
- weak acids can be consumed
- examples: citric acid, ethanoic acid, hydrochloric acid, sulphuric acid, nitric acid, phosphoric acid

ALKALIS
- have a slippery feel
- turn litmus paper from red to blue
- have a bitter taste
- are good electrical conductors
- neutralise acids
- react with ammonium salts to produce ammonia gas
- examples: sodium hydroxide, calcium hydroxide, beryllium hydroxide, calcium oxide, magnesium hydroxide, potassium hydroxide, ammonia solution

pH values of water from home

The students of 1C2 used a pH meter to measure the pH of the water taken from the taps at home. A total of 40 pupils conducted the test. The results are shown in the line graph below.

(Please click on the image for larger and clearer viewing.)

Based on the line graph, it is quite evident that the pH value of the water from most homes ranges between 6.51 and 7.00. And as none of the pH values hit 8.00, we can thus conclude that water in Singapore is safe for drinking. Reason being that weak acids are safe for consuming.

The pH meter

The picture below shows an example of a pH meter. It is an electronic instrument used to measure the pH value of a substance, consisting of a measuring probe (an electrode) connected to an electronic meter that measures and displays the pH value. The reading on the pH meter gives a reading up to accuracy 0.01, making the instrument much more exact in its reading.

To use the pH meter, you place the electrode into the solution and the pH value is read from the meter.

- DID YOU KNOW that the first commercial pH meters were made in America at around 1936?

Everyday substances

In the earlier post, you were showed how the universal indicator worked. The table here shows the pH values of some everyday substances.

(Please click on the image if it is not clear enough for viewing.)

As mentioned, acids have a pH value of less than 7 while akalis have a pH value of more than 7. This shows that items like milk, potatoes, tap water, soft drinks, lemons and grapefruit are acidic substances. Meanwhile, items like baking powder, soap, toothpaste, indigestion tablets, bleach and limewater are alkaline substances. Since neutral substances have a pH value of 7, we can therefore tell that distilled water is a neutral substance.

pH and universal indicator

A universal indicator is a mixture of a few other types of indicators. It may be used in the form of a solution or a paper. This indicator turns into different colours when added to different substances. Every colour will correspond to a pH value from 0 to 14. The only disadvantage of the universal indicator is that it can only give the approximate pH value of a solution.

The picture below shows how the indicator works. (Please click on the image if it is not clear enough.)


Acidic mixtures will have a pH value lesser than 7, while alkaline mixtures would have pH value of more than 7. Neutral mixtures will have a pH value of 7, meaning that they are neither alkali nor acid.

In order to get the accurate pH value of a substance, a pH meter can also be used. The electrode is dipped into the solution and the pH value is read directly from the meter.