When we want to say something has the properties of an acid, we use the adjective acidic. Testing, observing, measuring, recording, analysing, interpreting Investigation: Universal indicator paper and red cabbage indicator paper However, as there are only two key tasks in this chapter, you might progress through it at a faster rate than 1 week, and then move onto the next chapter dealing with the reactions of acids with bases, which requires more time.Īctivity: Measuring instruments and units The time indicated for this chapter is 1 week and so a suggested 1.5 hours has been allocated to each section. The strips will keep for a long time if stored in a dry place. When the paper has completely dried, cut it into strips (approximately 1 cm wide).You can also dry the paper with a hair dryer, but do not leave it in direct sunlight.
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The boiled cabbage slices can be eaten (or placed in the compost). Strain the juice off the cabbage slices into a large shallow dish.Remove the pot from the heat and let it cool completely.Boil it over low heat for approximately 30 minutes, adding water to keep the cabbage covered if necessary.Add just enough water to cover the cabbage slices.Cut a large red cabbage into thin slices and place it in a pot.To make red cabbage indicator paper, follow the instructions below: It would be best to add approximately 1 ml of each test solution to 2 ml portions of the red cabbage water. Red cabbage solution can also be used instead of paper.
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If you do not have universal indicator paper, but have universal indicator solution, you could easily adapt the activity in the following way: Instead of using paper, learners should add 2 - 3 drops of universal indicator solution to their test solutions, note and record the resulting colours. The investigation uses universal indicator paper and red cabbage paper to measure the pH of a selection of household products. There is an introductory activity on measurement - this helps to link this content to what learners might be doing in other subjects, such as Mathematics and Technology, and also to what they already know about measurement. There are two activities around pH measurement in this chapter: One is a paper activity and one is an investigation using indicators. While mixing any chemical reagents (unless otherwise specified of course), you should add the more reactive or concentrated solution to the less reactive or more dilute solution, for the same reasons as described for the addition of strong acids and bases to water.In this chapter, learners are introduced to the pH scale and learn how to measure and interpret pH values. This way, the rate of reaction (and thus also the heat evolution) will happen at a safe level and greatly reduce the risk of splattering.Īs a side note, this concept does not only apply to the addition of strong acids and bases to water. It is still important to do the addition slowly so that you only slowly increase the acidity/basicity of the solution. Even if you accidentally add the acid or base too quickly, at least the splattering will primarily be of water or dilute acid/base rather than splattering concentrated strong acid or base. On the other hand, if you slowly add the acid or base to water, you will never have a concentrated acid or base present to splatter as it will be rapidly diluted by the much larger amount of water.
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The reason for adding strong acids or bases to water rather than the other way around is that the dissolution/reaction of these compounds with water tends to be very exothermic and can result in splattering or even boiling of the strong acid or base, particularly if water is added to the concentrated acid or base.