Transcript Summary ppt
Acids and Alkalis Forming Acids Acids are formed from soluble non metal oxides. They have a ph range between 1 and 7 They turn pH paper of universal indicator red/orange/yellow Forming Alkalis Alkalis are formed from soluble metal oxides. They have a pH range between 8 and 14 They turn universal indicator and pH paper Dark green/blue/purple Examples of Acids and Alkalis Acids Hydrochloric Acid Nitric Acid Vinegar Orange Juice Sulphuric Acid Carbonic Acid Alkalis Sodium Hydroxide Toothpaste Ammonia Solution Calcium hydroxide Potassium hydroxide Bicarbonate of soda Neutral Substances A neutral substance is neither acid nor alkali. They have a pH =7 They turn universal indicator and pH paper green. Example – Water, Tea, Alcohol! Acid Rain Acid rain is formed when acidic gases dissolve in rain water. The main gas responsible is Sulphur dioxide! Oxides of Nitrogen can also contribute to the problem. Acid rain damages the environment: Eats away buildings, kills plants and fish, corrodes iron structures. Preventing Acid Rain! Remove Sulphur from fuels before you burn them. Reduce the amount of fossil Fuels you burn. Dissociation of Water Water exists mainly as molecules – however it sometimes splits into 2 ions – Hydrogen and Hydroxide. H2O(l) <—–> H+ (aq) + OH- (aq) Water will conduct electricity – slightly because it contains these ions. Water is neutral because it contains equal numbers of each ion. Conductivity Acids and Alkalis can conduct electricity because they contain ions. Acids = H+ ion Alkalis = OH- ion The stronger the acid or alkali is – the more ions it contains – the greater the conductivity! Diluting! When we add water to an acid or alkali– we dilute it – reduce the concentration of the ions! Acids – the concentration oh H+ ions gets less – the pH will increase – moving towards pH7 Alkalis – the concentration of OH- will get less – the pH will move down -towards pH 7 Electrolysis of Acids Acids will split up when you pass an electric current through them. This is because they contain ions – Hydrogen ions. When we electrolyse Sulphuric Acid the following happens: Bubbles of Hydrogen gas appear at the negative electrode. The H+ ions move to the – electrode – they gain electrons to form H2 gas 2H+ (aq) + 2 e —> H2 (g) Metal Hydroxides We can find out if a compound is soluble using p5 in the data book. Trends Metal hydroxides in Group 1 and 2 are soluble. E.g NaOH, KOH, Ca( OH )2 All other metal hydroxides are insoluble. e.g. Cu(OH)2, Zn(OH)2 Formula Mass This is the total mass of a compound. It takes into consideration the number and mass of each element in a compound. Steps Correct Formula – Use valency rules! Write down numbers of each elements in compound. Add in mass of element – use data book. Add up total mass. Formula Mass – example! Work out the formula mass of Calcium hydroxide. 1. Formula – Ca 2+ OHCross over – Ca (OH)2 2. Numbers of each element (1 x Ca) + (2 x O) + ( 2 x H) 3. Add in mass ( 1 x 40) + ( 2 x 16) + ( 2 x 1) 4. Add total mass 40 + 32 + 2 = 74 amu. The Mole! – Gram Formula Mass The mole is basically the formula mass in grams. The steps are required. Example – Calculate the mass of 1 Mole of Water Symbol – H2O Numbers of elements – ( 2 x H) + ( 1 x O) Add in Mass - (2x1) + (1x 16) Total Mass – (2x1) + 16 = 18 g 2 moles of water would be- 2 x18g = 32g More Calculations! n C V n = Number of Moles C = Concentration (mol/l) V = Volume (l) n=CxV C = n/V V = n/C Examples 1) Calculate – The number of moles if you have a solution of with 2 mol/l HCl in 100cm3 of water. n = CxV 2 x 100/1000 2 x 0.1 = 0.2 moles More! 2) Calculate the volume of water required to make a 2 mol/l solution of NaOH using 3 moles of the alkali. V = n/C =3/2 = 1.5 litres Even More! Calculate the concentration of solution made when 2 mol/l of acid dissolves in 50 cm3 of water. C = n/V = 2/(50/1000) = 2/ 0.05 = 40 mol/l