Table of Contents
Week 1 | English Grammar
Week 2 | English Grammar
Week 3 | English Grammar
Week 4| English Grammar
Week 5| English Grammar
Week 6| English Grammar
Week 7| English Grammar
Week 8| English Grammar
Week 9| English Grammar
Week 10| English Grammar
Week 11| English Grammar
Week 12| English Grammar
Week 13| English Grammar
The Periodic Table
The pH scale is a measure of how acidic or basic a solution is. It ranges from 0-14, with zero being the most acidic and 14 being the most alkaline. 7, being exactly in the middle, is what would be termed as neutral.
Any number less than seven is considered to be acidic – the lower the number, the more acidic the substance. 4 -6 would be considered ‘weakly acidic’.
Any number higher than seven is considered to be alkaline – the higher the number, the more alkaline the substance. 8-10 would be considered ‘weakly alkaline’
Substances which are very strongly acidic or alkaline tend to be reactive and can be even cause chemical burns, if not handled with care.
Measuring the pH
There are several different ways to measure the pH and find out whether a solution is acidic, alkaline or neutral. Some of these methods, such as Universal Indicator, will give an approximate numerical value on the pH scale, while others, such as Litmus paper, will only give a colour indication as to whether the solution is acidic, alkaline or neutral.
Universal indicator is a mix of several different indicators, which effectively allows it to show the whole range of different pHs.
It can be found in paper form, which is known as a pH test strip, or as a liquid solution which simply needs to be dropped onto a sample of the substance. After a couple minutes, there should be a colour change. The new colour should then be compared with the scale kit that is provided with the indicator and the pH can be estimated. Generally, the paper form is used when the solution is a dark colour already, while the liquid indicator is used on colourless samples.
Litmus paper can tell you if a solution is acidic or basic, but there is no ranging scale as there is in Universal Indicator. Instead, there will one of two colour changes to either red or blue and that is the result. If the Litmus paper is made wet, you can also measure the pH of gasses.
When Litmus paper is in neutral conditions, it will be purple.
When Litmus paper is in fairly strong acidic conditions (less than 4.5), it will be red.
When Litmus paper is in fairly strong alkaline conditions (more than 8.3), it will be blue.
KS3 Chemistry Questions – The pH Scale
1. What would 13 represent on the pH scale?
d. There’s no 13 on the pH scale
2. What number would represent a neutral substance?
3. Which of these is NOT a form of Universal Indicator?
a. Paper strip
4. Which of these is the most alkaline?
a. Bicarbonate of soda – pH 10
b. Water – pH 7
c. Sodium hydroxide – pH 12
d. Vinegar – pH 4
1. How does Litmus paper work?
2. Why is it important to know if something is strongly acidic or alkaline?
3. Lemon juice is a weak acid. Approximately where on the pH scale would it be found?
4. How is Universal Indicator different to Litmus paper?