Topic 3: Acids and Alkalis Flashcards
What type of dye does red cabbage contain?
A strong dye
What does red cabbage change and how?
Red cabbage changes colour depending on weather it is in contact with an acid or an alkali
What would red cabbage be called as a sort of chemical dye?
An indicator
Draw and label the apparatus needed to make a red cabbage indicator.
Bunsen burner, tripod, gauze, cabbage in boiling water, beaker, spotting tile
What is the method for making a red cabbage indicator?
- Set up a beaker containing 100ml of water and add some shredded cabbage.
- Using a stirring rod push the cabbage into the water.
- Bring to the boil and boil for 3-5 minutes.
- Turn off Bunsen and let apparatus cool.
- Using a filter funnel and filter paper, filter the mixture into a conical flask.
What is the method for testing the red cabbage indicator?
- Put a few drops of the substance into a dimple on a spotting tile.
- Add a few drops of the purple dye.
- Record the colour that appears on your results table.
What colour does the red cabbage indicator turn when you mix it with vinegar?
Red
What colour does the red cabbage indicator turn when you mix it with baking soda?
Green
What colour does the red cabbage indicator turn when you mix it with lemon juice?
Red
What colour does the red cabbage indicator turn when you mix it with dilute hydrochloric acid
Red
What colour does the red cabbage indicator turn when you mix it with dilute ammonia solution?
Green
What colour does the red cabbage indicator turn when you mix it with dilute sodium hydroxide?
Green
What colour does the red cabbage indicator turn when you mix it with water?
Purple
When is red cabbage indicator purple?
Red cabbage is purple when it is neutral but changes colour on addition of different solutions
When does red cabbage indicator turn red?
Red cabbage turns red on addition of acids e.g. lemon juice, hydrochloric acid and vinegar
When does red cabbage indicator turn green?
It turns green on addition of alkalis e.g. baking soda, ammonia solution and sodium hydroxide
Is red cabbage the only plant material that can change colour in acids or alkalis?
No
Name 2 other plant materials can change colour in acids and alkalis.
Red rose petals, beetroot, red onion skin
What are indicators?
Indicators are substances whose colour depend on whether they are an acidic or alkaline substance
What is the simplest indicator?
The simplest indicator is litmus which is red in acid and blue in alkalis
What is the method for using litmus paper?
- Take 2 strips of red litmus paper and cut it into 7 pieces
- For each of the seven substances, put a small piece of red litmus paper on a white tile and use the glass rod to place a drop of the substance on the litmus paper.
- Record what you observe in the second column of your results table.
- Repeat the above procedure for each of the substances using blue litmus paper
What colour does dilute hydrochloric acid turn on red and blue litmus paper?
Red : red
Blue : red
Is dilute hydrochloric an acid acid, alkaline or neutral?
Acid
What colour does sodium hydroxide solution turn on red and blue litmus paper?
Red : blue
Blue : blue
Is sodium hydroxide solution an acid, alkaline or neutral
An alkali
What color does sodium chloride solution turn on red and blue litmus paper?
Red : red
Blue : blue
Is sodium chloride solution an acid, alkaline or neutral?
Neutral
What colour does vinegar turn on red and blue litmus paper?
Red : red
Blue : red
Is vinegar an acid, alkaline or neutral?
Acid
What colour does washing soda solution turn on red and blue litmus paper?
Red : blue
Blue: blue
Is washing soda solution an acid, alkaline or neutral?
Alkali
What colour does water turn on red and blue litmus paper?
Red : red
Blue : blue
Is water an acid, alkaline or neutral?
Neutral
What colour does ammonia turn on red and blue litmus paper?
Red : blue
Blue : blue
Is ammonia acid, alkaline or neutral?
Alkali
What do acidic substances do to red and blue litmus paper?
Makes blue litmus paper turn red
No effect on red litmus paper
What do alkaline substances do to red and blue litmus paper?
Makes red litmus paper turn blue
No effect on blue litmus paper
What do neutral substances do to red and blue litmus paper?
No effect on either type of litmus paper
Litmus paper is r_ _ in a _ _ _ and b_ _ _ in a_ _ _ _ _
Litmus paper is red in acid and blue in alkali
What does litmus paper tell us?
If a substance is acidic, alkaline or neutral
What does litmus paper not give us?
Any indication of how strong the acid or alkali is
What can a universal indicator tell us?
How strongly acidic or alkaline solutions are
What do universal indicators contain?
A mixture of dyes and so can turn a whole range of colours
What do we much the colour of the universal indicator to?
A pH number
What is the pH number shown on?
The pH scale
When writing pH remember that the p is always a s____ l_____ while the H is always a C______ L_____
When writing pH remember that the p is always a small letter while the H is always a Capital Letter
On the pH scale what pH do acids have?
Less than 7
On the pH scale what pH do neutral substances have?
7
On the pH scale what pH do alkalis have?
Greater than 7
What is the method for measuring pH using universal indicator?
- Tear the strips of universal indicator paper into 12 pieces.
- For each of the 12 substances, put a small piece of universal indicator paper on a white tile and use the glass rod to place a drop of the substance on the universal indicator paper.
- Record the colour of the universal paper and use the colour chart to decide the pH of the substance
- Record your results in the pH column
- Universal indicator paper only gives an approximate value for the pH. After you have finished the experiment, your teacher will tell you the actual pH of each substance, which you should write in your table
- Finally describe each substance as a strong/weak acid, neutral or weak/strong alkali
How can we distinguish a strong acid?
If the pH is well below 7, pH = 1 to 2
How can we distinguish a weak acid?
If pH is only a few units below 7, pH = 3 to 6
How can we distinguish if something is neutral?
If pH is 7, pH = 7
How can we distinguish a weak alkali?
If pH is only a few units above 7, pH = 8 to 11
How can we distinguish a strong alkali?
If pH is well above 7, pH = 12 to 14
What is the colour of universal indicator paper, actual pH and description of dilute hydrochloric acid?
Colour of universal indicator paper = red
Actual pH = 1
Description = strong acid
What is the colour of universal indicator paper, actual pH and description of sodium hydroxide solution?
Colour of universal indicator paper = purple
Actual pH = 13
Description = strong acid
What is the colour of universal indicator paper, actual pH and description of sodium chloride solution?
Colour of universal indicator paper = green
Actual pH = 7
Description = neutral
What is the colour of universal indicator paper, actual pH and description of vinegar?
Colour of universal indicator paper = orange
Actual pH = 4
Description = weak acid
What is the colour of universal indicator paper, actual pH and description of washing soda solution?
Colour of universal indicator paper = blue
Actual pH = 11
Description = weak acid
What is the colour of universal indicator paper, actual pH and description of water?
Colour of universal indicator paper = green
Actual pH = 7
Description = neutral
What is the colour of universal indicator paper, actual pH and description of ammonia solution?
Colour of universal indicator paper = blue
Actual pH = 10
Description = weak alkali
What is the colour of universal indicator paper, actual pH and description of lemon juice?
Colour of universal indicator paper = orange-red
Actual pH = 4
Description = weak acid
What is the colour of universal indicator paper, actual pH and description of baking soda solution?
Colour of universal indicator paper = green-blue
Actual pH = 8
Description = weak alkali
What is the colour of universal indicator paper, actual pH and description of sugar solution?
Colour of universal indicator paper = green
Actual pH = 7
Description = neutral
What is the colour of universal indicator paper, actual pH and description of milk of magnesia?
Colour of universal indicator paper = green-blue
Actual pH = 8
Description = weak alkali
What is the colour of universal indicator paper, actual pH and description of toothpaste?
Colour of universal indicator paper = blue
Actual pH = 9
Description = weak alkali
What do you think happens when you add an acid to an alkali?
It becomes neutral
When a wasp stings it injects a small amount of alkali under your skin. How might you treat the wasp sting with a household substance?
Treat it with an acid e.g. vinegar or lemon juice
What reaction takes place when we add an acid to an alkali?
Neutralisation
Why is it called neutralisation when we add an acid to an alkali?
It is called neutralisation because water is produced
Is a bee sting an acid or alkali, what can it be treated with and give an example.
Acid
Treated with an alkali
Example: baking soda
Is a nettle sting an acid or alkali, what can it be treated with and give an example.
Acid
Treated with an alkali
Example: juice of a dock plant
Is indigestion an acid or alkali, what can it be treated with and give an example.
Acid
Treated with an alkali
Example: antacid
Is tooth decay an acid or alkali, what can it be treated with and give an example.
Acid
Treated with an alkali
Example: toothpaste
What is the method for a neutralisation reaction?
- Measure 20 cm³ of acid and put it in a conical flask.
- Add 4 drops of universal indicator solution.
- Record the colour and pH of the liquid.(red, pH value of 2)
- Add 5 cm³ of sodium hydroxide and shake carefully.
- Record the colour and pH again.(red, pH value of 2)
- Repeat this until; 15 cm³ have been added.pale red, pH value of 2/3
- Add drops of sodium hydroxide using a dropper until the solution is neutral, that is the colour of the solution goes green.(it has turned green, if more is added it will turn purple)
- Add more sodium hydroxide, and note what happens to the colour
Give an explanation for invisible ink?
The invisible ink we used was really a colourless indicator called phenolphthalein. When the page was sprayed with an alkali then the indicator turned it pink and we were able to see the message
What is the name of the acid in your stomach?
Hydrochloric acid
Match each problem with the correct neutralising treatment:
a. Indigestion caused by too much A. Rub with leaves of
stomach acid. alkaline plant
b. Acid rain pollutes lakes and B. Regular brushing with alkaline
poisons wildlife. toothpaste
c. Power stations produce gas C. Antacid tablets
which forms acid rain
d. Nettle sting contains acid which D. Calcium carbonate neutralises
irritates skin acidic gas before it is released
e. Mouth bacteria produce acid E. Calcium carbonate reduces
from sugary foods. acidity of water
a. & C.
b. & E.
c. & D.
d. & A.
e. & B
Weak acids, like lemon juice and vinegar, taste _________
Weak acids, like lemon juice and vinegar, taste sour
Strong acids can be _____________
Strong acids can be corrosive
Acids turn blue litmus paper _______
Acids turn blue litmus paper red
Acids have a pH of _______ than ___________
Acids have a pH of less than 7
Acids can be ______________ with alkalis
Acids can be neutralised with alkalis
Alkalis feel _________
Alkalis feel soapy
Strong alkalis are _____________ __________
Strong alkalis are corrosive ( caustic )
Alkalis turn red litmus paper ______
Alkalis turn red litmus paper blue
Alkalis have a pH of _______ than _________
Alkalis have a pH of more than 7
Alkalis can be _______________ with acids
Alkalis can be neutralised with acids
You probably have used hydrochloric acid in your school laboratory without wearing breathing apparatus. Why do you think fire-fighters need to wear breathing apparatus?
This is for a concentrated solution producing dangerous fumes
What type of chemical must soda ash be, if it was used to neutralise the acid?
An alkali
How could you know when enough soda ash has been added?
Test the pH of the mixture which will be neutral (pH 7) when enough soda ash has been added
Why do you think soda ash was chosen rather than other possible chemicals which could neutralisé the acid?
A solid is more concentrated than a solution. If excess is left behind it is washed away which means it will not be very harmful.
Why do you think it was necessary to neutralise the acid? Why not just wash it away with water?
The acid would be washed into drains that eventually run into rivers/lakes/seas etc. and could kill aquatic life such as fish. It should be neutralised to get rid of the acid - if only add water then it is just diluted but still there.
Suppose you were the journalist who wrote this story, and you decided to write a few more sentences to explain to the general reader why the acid was neutralized. What would you write?
Acids are corrosive and can cause burns/damage to the skin etc.
If acid was to get into rivers it would kill fish
In order to support life what pH do lakes roughly need to maintain?
pH of about 7
What has the lake at Hillsborough Park become?
Acidic
What apparatus do you need for treating a lake effected by acid rain?
Beaker (100 cm³), measuring cylinders, pH meter and probe, lake water sample, sodium hydroxide (alkali)
What is the method for treating a lake effected by acid rain?
- Measure out 20 cm³ of the first sample.
- Place the sample in the 100 cm³ beaker.
- Measure the sample’s pH using the pH probe connected to the data logger.
- Record the results in a table.
What is the conclusion for treating a lake effected by acid rain?
At the start the lake water was acidic (pH =1.6). As alkali was added the pH value increased and when 20 cm³ of alkali was added the pH value increased rapidly. As more alkali was added the water turned alkaline (pH greater than 7).
What is a chemical that has a pH greater than 7?
An acid
What is a chemical that has a pH greater than 7 and dissolves in water?
An alkali
What is a special chemical that changes into different colors and acid and alkali solutions?
Indicator
What is a chemical with a pH of 7 that is not a n acid or an alkali?
Neutral
What is the chemical reaction between an acid and an alkali?
Neutralisation
What is the range of values that shows how strong or weak an acid or alkali is?
pH scale
What is the indicator that shows the pH value of a chemical?
Universal indicator
What is an indicator that turns red with indicator and blue with an alkali?
Litmus
What is a value that is given to a substance to indicate how strong or weak an acid or alkalis is?
pH number
Acids are the chemical opposites of what?
Alkalis
Indicators are one _________ in acids and another _________ in alkalis.
Indicators are one colour in acids and another colour in alkalis.
Litmus paper is a useful indicator. It turns red in ________ and blue in __________. In neutral solutions it remains ________.
Litmus paper is a useful indicator. It turns red in acids and blue in alkalis. In neutral solutions it remains green .
Match each of the pH numbers with the correct statement:
a. pH 6 A. strong acid
b. pH 1. B. strong alkali
c. pH 14. C. weak acid
d. pH 8. D. weak alkali
a. & C.
b. & A.
c. & B.
d. & D.
Complete this sentence:
Universal indicator is more useful than litmus paper because ………
Universal indicator is more useful than litmus paper because it shows how strong or weak an acid or alkali is using something called a pH scale. This is because litmus paper only indicates whether a substance is an acid or alkaline.
Discuss an everyday neutralisation reaction?
Indigestion is caused by too much acid in the stomach and can be neutralised ed by taking antacid tablets which contain a weak alkali
Tooth decay is caused when you eat too much food with acid in it, but can be neutralised by using toothpaste (alkali)
On the pH scale what colour is pH 1?
Red
On the pH scale what colour is pH 5?
Orange
On the pH scale what colour is pH 6?
Yellow
On the pH scale what colour is pH 7?
Green
On the pH scale what colour is pH 8?
Dark green
On the pH scale what colour is pH 9?
Blue
On the pH scale what colour is pH 10-11?
Dark blue
On the pH scale what colour is pH 12-14?
Purple
A vegetable patch needs to be neutral, what would Andy need to add to it? Explain your answer.
Andy would need to add acid to pH above 7 and add alkali to pH below 7 so that they will all be neutral.
Is pH 4 or 9 most acidic?
pH 4
Is pH 6 or 8 most alkaline
8
Is pH 8 an alkaline or acid, explain your answer?
It is slightly alkaline because it has a pH above 7
