Chapter 7- Science

Science notes:Chapter 5:7.1-Acids and AlkalisAcids Acids and alkalis are everywhere. Some acids and alkalis are dangerous. Dangerous chemicals have hazard warning labels. Acids and alkalis are chemical opposites. They cancel each other out when they are mixed together. Lemons and Oranges- Sour-Citric Acid( Weak Acid) Examples of acids: Hydrochloric acid, nitric acid and sulfuric acid. Acids have a sharp, sour and tangy taste. It is found almost everywhere, even in food. Strong acids are corrosive. If acids get onto our skin, our skin dissolves it and you get chemical burns. Acids and alkalis can be diluted with water, this makes them less dangerous. Dilute acids are still harmful or irritant. If you spill acid, wash the area with lots of water, the water will dilute the acid. Alkalis Alkali-Cleaning products....If it is in contact with skin, then skin feels soapy and you get  a chemical burn. Strong alkalis are corrosive( Sodium hydroxide). Alkalis and acids are dangerous if they come in contact with your eyes. Common alkalis found are sodium hydroxide, potassium hydroxide and calcium hydroxide. Working safelyStand up, wear safety glasses, replace bottle top as soon work is finished and take of the bottle top and place the bottle upside down on the work surface while working.Q&A1. Lemon is a fruit which contains acid.2.Lemons and limes are sour.3. Corrosive means dangerous, if corrosive acid or alkali is in contact with our skin we get chemical burns.4. If you spill acid, you should wash it with a lot of water so that the acid is completely diluted by the water.

7.2-Is it an acid or an alkali?An indicator changes colour in an acid or alkali.Some plant materials mage good indicators.Litmus is red in acids, purple in neutrals and blue in alkalis.Substances that are neither acid nor alkali are called neutral.Red cabbage, blackcurrant and beetroot can be used to make a good indicator.Litmus is a very common indicator(dye).Q&A1. The indicator changes colour when it is put in the liquid, it turns blue in alkalis and red in acids. This indicates the difference in acids and alkalis.2. Red cabbage juice turns red when it is put in lemon juice.3. Litmus turns blue when it is put in sodium hydroxide.4. Litmus turns red when it is put in an acid.5. Water is neutral because when litmus is put into water it turns purple. Litmus turns purple when it is put in a neutral substance.7.3- The pH ScaleThe pH scale measures how acidic or alkaline a substance is.Universal indicator is an indicator that shows how acidic or alkaline a substance is. It can turn into many different colours to show the pH of a substance.(The colour it changes to is matched with the colour on the pH scale to show its strength)Common valuesstrongly acidic-red-1weakly acidic-yellow-4neutral-purple-7weakly alkaline-blue-10strongly alkaline-purple-13The chart below shows the Universal Indicator.Q&A1. The pH scale measures the strength of a acid or an alkali.2. The pH of a neutral solution is 7.3. A liquid with a pH of 1 is a strong acid.4. The pH range of strong alkalis is 11-14 pH.5.The colour of the Universal Indicator in a liquid with a pH of 9 would be blue.6. The Universal Indicator goes red and yellow in acids.

7.4- NeutralisationAcid and alkali can cancel each other out.When they react together, they neutralise each other. This is neutralisationTo neutralize an alkali you must add the exact right amount of acid.If you add too much acid, the liquid turns into an acidic liquid. If too less acid is added, the liquid remains an alkaline liquid.Burette can be used to drop the acid slowly or you can pour it slowly, you can also pour it with the help of a dropper.Rainbow in a tube-top -acid- Since the acid was put at the end on top, the acid was strong then it goes down and mixes with water to become weak(red and yellow)bottom-Alkaline- Since the alkaline was put first at the bottom it was purple and then towards the middle it was blue and then lighter blue.middle-Neutral-The acid and alkali cancelled each other and reacted to neutralise each other producing a neutral liquid(green)Q&A1. The colour of the Universal Indicator is green when the solution is neutral.2.When an acid and alkali are mixed, they cancel each other out, neutralising each other. This process is called neutralisation.3. The pH at the top of the test tube is from 1-5 ( strongly acid to weakly acid).4. The pH at the bottom of the test tube is from 9-13( weakly alkaline to strongly alkaline)5. The most strongly alkaline part is at the bottom of the test tube.7.5- Neutralisation in action Antacids are used to neutralise hydrochloric acid produced by the stomach for digestion. Toothpaste is an alkali an helps to neutralise the acid in the mouth. A neutralisation reaction can be used to change the pH of lakes and soils. The bacteria in our mouth feed on the remaining food pieces left on our teeth. This produces acid and the toothpaste helps to neutralise it since it an alkali. In some of the places on Earth, the air has harmful chemicals present. This changes the pH of rivers and lakes causing acidic rains. The acid rain harms the trees , plants and animals that live in that area. Some countries drop alkali onto the lakes to reduce the level of acid in it. In some areas the land is very acidic. Therefore, plants are not able to grow well, which is why farmers rub lime over the land to neutralise the acid. Q&A1. Toothpaste is alkaline because it is used to neutralise the acid present in the mouth .2. The acid present in our mouth is produced by the bacteria which feeds on the food pieces left in our mouth.3. An alkaline substance is dropped in lakes in some places to neutralise the excess acid in the lakes.4. Farmers spread lime on the ground to neutralise the excess acid present in the ground.

7.6- Investigating acids and alkalis Scientists put a question for investigation in a way that can be tested. An investigation must be planned to make it a fair test. Results can be recorded in a table. Results are used to provide evidence to answer questions being investigated. Model is used to represent something. It represents and gives the result that the actual specimen is supposed to give, but it is just a representation. Variables are the things that change in an experiment. Q&A1. a)The amount of hydrochloric acid put and the drops of Universal Indicator. Even  the size if spatula.b) The type of powder.c) The pH of the substance.2. a) The most effective powder is Powder B.The least effective powder is Powder C.b) I think there is enough evidence to prove my answer in part a) correct.3. Powder is the most effective powder.4. The result of Powder B in the 1st try seems wrong.5. The students must have miscounted the number of spatulas of powder.End of Unit7.1 a) Indicatorb) Redc) Purple7.2Words associated with acids- makes Universal Indicator turn red pH2 sour lemon juice Words associated with alkalis- makes Universal Indicator turn blue pH9 toothpaste soapy 7.3a) The warning was important because if there would be an accident then people passing by would not be hurt ,but if it was not there, they could come in contact with it unknowingly.b) If acid is spilt on the ground, then it should be diluted with water because the it gets diluted and becomes less harmful.7.4a) The solution was blue in colour at the start.b) The colour of the solution at the end was green.c) The acid and alkali were equal in strength. It is because an equal amount of both acid and alkali were put to make the solution neutral. d)      

7.1

7.2+7.3

7.4+7.5

7.6+End of unit