Yr 8 Mid-year Revision Answers

Lab Rules Wear safety glasses when working with glass, chemicals or heat, or when instructed to by the teacher because safety glasses protect your eyes from being damaged by glass, reactive chemicals (like acids) or hot materials. Put bags in one of the cubby holes because bags on the ground can be tripped over and cause injury Do not touch anything in the room on the side benches, unless instructed to by a teacher equipment in the science lab can be dangerous. It could be somebody's experiment. Do not sit on the benches or side benches as there may be acid or other dangerous chemicals spilled on the bench that has not been cleaned up properly. Always push chairs in when standing up as someone may trip over your chair and be injured. Report any breakages immediately as broken lab gear is dangerous and could cause injury. It must be cleaned up quickly. Do not bring food or drink in to the laboratory there may be things in the lab that will be harmful if ingested, like microbes or acids wear shoes to science as there may be broken glassware on the floor that may cause injury

Lab Equipment Measuring Cylinder for accurately measuring volume

Beaker – for holding, mixing and pouring liquids

Test tube – for holding and mixing small quantities of liquids or solids.

Gauze mat – for holding beakers/crucibles on the tripod above the Bunsen

Funnel – for safely pouring liquids into flasks or test tubes or for separating solids and liquids while filtering.

Bunsen burner – for heating.

Retort stand and clamp – for holding equipment in position.

Test tube holders – for holding test tubes in a Bunsen flame.

Tongs – for holding beakers/crucibles/evap orating dishes when they are hot.

Bunsen Burner

Scientific Method Title – what it is about Aim - what are you investigating Method – a step by step plan of how you will investigate the problem Results – presented in a table with ruled lines and headings and on a graph. Conclusion – what you found out. Scientific ideas – why you got the results you did Evaluation – how reliable are your results.

Graphs A bar graph is used when investigating categories e.g. bounce height on different surfaces. A line graph is used when looking at relationships between two sets of numbers. E.g. bounce height vs drop height. All graphs require a title and must be clearly labelled.

Tables Time (min)Temperature (⁰C)

Properties of acids Acids are corrosive – they react with metals, some stones, alkalis, teeth and tissues (such as your skin or mouth). They can be harmful! Acids taste sour. We can eat some acids if they are weak. Acids contain hydrogen ions. (Small particles that do the reacting).

Properties of Alkalis Alkalis are corrosive. They dissolve grease and fats (including the ones in your skin). So they are found in cleaners, dish washing powder and soaps. They feel soapy on your skin. They neutralise acids.

Acids and Alkalis Indicators Indicators can be used to show which things are acids and which are alkalis. Indicators indicate when an acid or alkali is present by changing colour. There are many different types of indicators. Litmus turns blue in alkali and red in acid. It is made from lichens which grow on tree bark & rocks. Universal indicator is a mixture of different indicators and turns different colours depending on how acidic or alkaline a solution is.

Red Cabbage 1.Rip a leaf of red cabbage into 2cm long pieces and place in a mortar. 2.Add 20mL of ethanol and a pinch of sand to the mortar. 3.Use the pestle to carefully grind the pieces of leaf until the colour is extracted. 4.Add 1mL of the liquid (using a pipette) to each of 3 test tubes containing 1ml of hydrochloric acid, 1mL of sodium hydroxide and 1mL of water respectively. 5.Record the initial colour of the red cabbage indicator and the colour of the indicator in each of the test tubes. 1.Rip a leaf of red cabbage into 2cm long pieces and place in a beaker with 100mL of water. 2.Heat over a Bunsen for 5min. 3.Add 1mL of the liquid (using a pipette) to each of 3 test tubes containing 1ml of hydrochloric acid, 1mL of sodium hydroxide and 1mL of water respectively. 4.Record the initial colour of the red cabbage indicator and the colour of the indicator in each of the test tubes.

Acid Rain Acid rain is caused by the burning of fossil fuels in factories, car engines and power plants. These release gases such as carbon dioxide, the nitrous oxides and the sulfurous oxides into the atmosphere where they react with water to form acid rain. Acid rain is a problem because it attacks steel structures and certain statues. It lowers the pH in rain causing asthma in people. It lowers the pH of lakes killing life within them and kills forests.

Neutralisation To understand that solutions that are not acids or alkalis are said to be neutral. To understand that we can use an acid to neutralise an alkali solution and we can use an alkali to neutralise an acid solution.

Acids and Teeth (copy the black writing) When you eat food often remains between your teeth.. Chemical reactions occur, and the bacteria give off weak acids as waste products. The mixture of bits of food, bacteria, acids and saliva that stick to your teeth is called plaque (plark). The inside of the tooth is made of a softer substance called dentine. Bacteria in your mouth then feed on this food, grow and multiply. The acids released react slowly with your teeth, causing tooth decay. Plaque covers the tooth enamel which starts to decay. The acids and bacteria get into the dentine and the tooth becomes damaged very rapidly.