3/26/2011. explosion

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1 Chemistry Acids and Bases Year 10 Study of Chemicals and how they react Everything is made of chemicals They are made of elements. There are over 100 elements Acids are common Some are dangerous and can burn your skin Some are safe to eat and drink Stomach acid helps digest food What are Acids? explosion Acids Definition A group of compounds which behave similarly All have low ph Turn Litmus paper RED All donate H + ions in aqueous solution Examples Hydrochloric HCl Sulfuric H 2 SO 4 Nitric HNO 3 Ethanoic CH 3 COOH Acids What are Bases (Alkalis)? A dilute acid has lots of water and a small amount of acid A concentrated acid has lots of acid and not much water so must be handled carefully A strong acid releases lots of H + A weak acid releases fewer H + In our home we often use bases to clean things. Eg Bleach and toothpaste Some things are not acids or bases, we say that they are neutral. Eg Water 1

2 Bases Definition A family of compounds that behave similarly Have a high ph Turn litmus BLUE All donate OH - Examples Ammonia NH 3 Sodium Hydroxide NaOH What does ph measure? ph Measures the concentration of H+ ions in a substance. H+ = Hydrogen with a positive charge The more H+ the lower the ph PH SCALE (COPY IN NOTES) Measuring acid strength? To decide if something is an acid or a base we can use an indicator. Litmus and Universal Indicator are examples of indicators. They change colour depending on if they are in an acid or a base. Working with Indicators Red litmus turns BLUE in the presence of Bases Blue litmus turns RED in the presence of acid Acids and bases react together in a NEUTRALISATION reaction Acid Reactions Acid + Base Salt + Water Acid + Metal Salt + Hydrogen Acid + Carbonate Salt + Water + Carbon Dioxide Hydrochloric acids (HCl) form CHLORIDE salts Nitric acid (HNO 3 ) forms NITRATE salts Sulfuric acid (H 2 SO 4 ) forms SULFATE salts 2

3 Dissociation in Water Dissociation means completely breaking down into ions in water Strong Acids Completely Dissociate in water to form ions. Amphoteric Substances Substances that can act as an acid or a base Many metals fit in this category Zinc, Tin, Lead, Aluminum, Beryllium Bases and Weak Acids do not dissociate completely Consider Causes natural human Effects buildings flora fauna health Prevention/Solution Acid Rain Antacid Investigation NZ facts % population get heartburn /GERD $9m on 1 brand! 3 rd most widely prescribed medicine Which brand is the best? Identify Unknown Solutions Review Click Here For Review 3

4 Rates of Reaction Factors increasing the rate of reaction Metals/periodic table, Element, compound, exo/endo Surface area Concentration Temperature Catalyst/Enzyme Pressure Method Results 1. Collect the 4 substances to be tested 2. Place a drop of the first substance in the spotting tile 3. Test the substance with a drop of universal indicator 4. Record the result 5. Repeat steps 1-4 with the remaining 3 substances Substance Hydrochloric acid Ammonia Water Sodium Hydroxide Universal indicator colour Experiment write up Title Working with Indicators Aim To find out what happens when. Method As previous slide, short bullet point Diagram Half page, labels, straight lines Results Draw your table Conclusion Write about what you learnt from the experiment. Universal indicator turns blue in bases, red in acids and green when solutions are neutral. was a base because it turned blue when we added indicator.. Was an acid as it turned red when we added indicator.. Was neutral as it turned green when we added indicator Investigate an Acid Vinegar is an acid Add some powders to vinegar and OBSERVE what happens Dissolve powder is soluble Doesn t dissolve powder is insoluble Fizzing reaction is occurring gas given off Heat does it get hot or not Smell gas given off Colour change 4

5 Experiment time! Method 1. Collect 5 test tubes in a test tube rack 2. Put 1 spatula of either sugar, salt, baking soda, flour, washing powder into each test tube 3. Collect vinegar in a 50ml beaker 4. Add 5ml vinegar to a test tube and observe what happens 5. Record results in a table 6. Repeat step 4 and 5 until all test tubes are tested Substance Sugar Salt Etc. Results Observations (Dissolves, fizzes, smells etc.) Experiment write up Title Reactions with Acid Aim To find out what happens when. Method As previous slide, short bullet point Diagram Half page, labels, straight lines Results Draw your table Conclusion Write about what you learnt from the experiment. Some substances are able to dissolve completely and form a solution. Others will not dissolve and are insoluble. Acid Extension Investigating Evaporation Test series of fruit juices with indicator Which has most acid Rot teeth Write up When water is heated it turns from a liquid into a gas (steam) This is called evaporation Some things dissolved in the water will be left behind when the water is heated Evaporation can be used to separate some solutions 5

6 Method 1. Place 2g of salt and 10ml of warm water into a test tube 2. Place thumb over the top and shake to dissolve. 3. Pour 5ml of the salt solution into an evaporating dish 4. Light the Bunsen and turn to a blue flame 5. Heat the mixture until almost all the water has disappeared. 6. Observe and record what happens Experiment write up Title Investigating Evaporation Aim To find out what happens when. Method Short bullet points Diagram Half page, labels, straight lines Results Describe what happend Conclusion Write about what you learnt from the experiment. Testing for Glucose Glucose is a sugar Benedict s solution is used to test for glucose Add Benedict s to the sample and heat, it turns ORANGE if glucose is present Forensic Scientists Police often need scientists to help determine the cause of death This person died holding 4 bags of white powder (salt, glucose, starch, baking soda) You must investigate the substances and identify what they are Design your Experiment You have: Vinegar Water Benedict s solution Unknown Solutions You have been given four solutions (glucose, salt, baking soda and vinegar) The labels have fallen off! Design an experiment which will allow you to identify the solutions Evaporation Benedict s Universal indicator Water 6