INDICATORS AND pH

Indicators and pH

7th gradeTeachers: Ms. Yohann Galvez Ms. Melisa Rivera Ms. Francisco Gaviria

Activate 1 book

Learning objectives

Use the pH scale to measure acidity and alkalinity

Describe how indicators categorise solutions as acidic, alkaline, or neutral.

Key words

indicator

litmus

pH scale

neutral

universal indicator

Watch and take notes. Share with the class.

Explain what pH means.

How many times more acidic is a substance with a pH of 5 than pure water?

How many times more alakaline is a substance with a pH of 10 than pure water?

How acidic? How alkaline?

Which is more acidic, vinegar or stomach acid?

A universal indicator is a mixture of dyes. It changes colour to show how acidic or alkaline a solution is.

Universal indicator turns orange in vinegar. It turns red in stomach acid.

How can you find out if a solution contains an acid or an alkaline?

An ___________ contains a _______ which turns a _______________colour in _____________ and ________________ solutions.

alkaline

acidic

indicator

dye

different

LITMUS INDICATOR

Acidic Solution

Alkaline Solution

Red Litmus turns blue

Blue Litmus turns red

Books page 102

Which plants make good indicator?

The table shows the colours of some plant indicators in acidic and alkaline solutions.

What is the pH scale?

The pH scale is a measure of how acidic or alkaline a solution is.

The __________the pH, the __________acidic the solution.

higher

lower

The _______the pH, the _______alkaline the solution.

more

more

ACIDITY

ACTIVITY.

Amie collected the data in the table. Use the data to list the names of the solutions in order of increasing acidity, starting with the least acidic.

Books page 103

When a solution is neither ___________ or _______________ it means it is ____________. The ___________ of a ____________ solution is exactly 7.

neutral

alkaline

acidic

neutral

pH

SUMMARY QUESTIONS

Activate 1 book, page 103, ex. 1

Copy the sentences below, choosing the correct bold words.

Adding an acid to red litmus paper makes the litmus paper go red / blue. On the pH scale, acids have a pH of less than / more than 7. The higher the pH, the more / less acidic the solution. A solution is alkaline if its pH is more than / less than 7. A solution of pH of 7 / 0 is neutral.

SUMMARY QUESTIONS

Activate 1 book, page 103, ex. 2

Read and explain.

John has a solution. It turns yellow when he adds red-cabbage juice. Predict what colour the solution would turn if he added hibiscus-flower juice. Explain your answer.

SUMMARY QUESTIONS

Activate 1 book, page 103, ex. 3

Create a chart

Using information from this page, create a chart to show the colours of dilute sodium hydroxide solution in five different indicators.

NEUTRALISATION

7th gradeTeachers: Ms. Yohann Galvez Ms. Melisa Rivera Ms. Francisco Gaviria

Learning objectives

Describe how pH changes neutralization reactions.

State examples of useful neutralisation reactions

Indigestion tablets neutralise stomach acid.

Key words

neutralisation

base

Have you ever had a stomachache? Did you take an indigestion tablet?

EXTRA STOMACH ACID

= the pH gets closer to 7

neutralises

AN INDIGESTION TABLET

Which substances neutralise acids?

Bases

(sodium hydroxide - calcium oxide - copper oxide)

A soluble base (in water) is an alkali.

pH changes in neutralisation reactions

Read Gwil's experience with neutralisation reaction (Books, page 104). State what volume of sodium hydroxide solution was needed to neutralise acid.

How is neutralization useful?

Read Deepa's experience with neutralisation reaction (Book, page 105). Then answer: How did neutralisation help Deepa? Explain in your own words.How can neutralisation reaction help acidic lakes? Read about it in your books, page 105.

SUMMARY QUESTIONS

Copy and complete the sentences below:

Explain two gardeners why they should measure soil pH, and how they can change soil pH.

The soil in Freya's farm is pH 7.0. Use data from this page to suggest three crops she could try growing. Explain your choices.

A base cancels out an acid in a ___________ reaction. An alkali is a soluble ___________. you can measure pH with an ________ or a pH probe attached to a ________ logger.

Thanks!