1. Yr 10 Chemistry Acids and Bases

2.  Calculate the new concentration if I ADD 200ml of water to 300ml of 2M HCl. Starter

3.  TO KNOW the term acid, base, pH, titration, dissociate.  TO BE ABLE to do calculations for titrations  TO UNDERSTAND how the pH scale works. Objectives

4.  Acids start with H in there formula.  Bases usually have OH at the end of their formula. What is an Acid and Base?

5. Neutralization  Acid + Hydroxide  Salt + Water HCl (aq) + NaOH (aq) è NaCl (aq) + H 2 O (l) HNO 3 (aq) + NaOH (aq) è NaNO 3 (aq) + H 2 O (l) CH 3 COOH (aq) + NaOH (aq)  NaCH 3 COO (aq) + H 2 O (l) Acid + Reactive Metal  Salt + Hydrogen Gas Na(s) + HCl(aq) → NaCl(aq) + H 2 (g) Zn(s) + 2HCl(aq) → ZnCl 2 (aq) + H 2 (g)

6. Complete and Balance the Following Equations Note: The more unreactive metals (e.g. Cu and Pb) do not react with acids)

7. Bases in Solution  Remember, just the soluble bases are considered to be alkalis and when added to water release an OH ion  K 2 O (s) + H 2 O (l) ⇌ 2K + (aq) + 2OH - (aq)  NH 3(aq) + H 2 O (l) ⇌ NH 4 + (aq) + OH - (aq)  CO 3 2- (aq) + H 2 O (l) ⇌ HCO 3- (aq) + OH - (aq)  HCO 3 - (aq) ⇌ CO 2 (g) + OH - (aq)

8. The pH Scale  Stands for power of Hydrogen (it is the concentration of hydrogen ions and equal to the power of ten with the sign reversed) Scale between 1 and 14 pH 7 is neutral Acids are from 0 to 6.99 When acids are in solution they ‘dissociate’ to to become an anion and hydrogen ions (H+). It is the amount of H+ that determines how acidic a solution is.

9. pH[H+] (mol dm -3 ) [H+] (mol dm -3 ) 010 0 1 110 -1 0.1 210 -2 0.01 310 -3 0.001 410 -4 0.0001 510 -5 0.00001 610 -6 0.000001 710 -7 0.0000001 What is happening to the hydrogen ion concentration with each decrease in pH unit?

10.  The pH scale is a LOGARITHMIC SCALE.  One change in pH is a x10 jump in H+  Two changes in pH is a x100 jump in H+  Three changes in pH is a x1000 jump in H+  etc

11. pH[H+] (mol dm -3 ) [H+] (mol dm -3 ) 810 -8 0.0000001 910 -9 0.00000001 1010 -10 0.000000001 1110 -11 0.0000000001 1210 -12 0.00000000001 1310 -13 0.000000000001 1410 -14 0.0000000000001 When we put a base into water, The OH- soaks up the H+ present (to produce water) reducing the H+ concentration.

12. 1. Black coffee has a pH of 5 and toothpaste has a pH of 8. Identify which is more acidic and deduce how many times the [H+] is greater in the more acidic product. (Total 2 marks)

13. Indicators IndicatorAcidBase Methyl Orangeredyellow Phenophthaleinclearfuchsia Universal Indicator red/orange/ yellow blue/purple Bromthymol Blue yellowblue Litmus PaperRed  BlueBlue  Red

14.  Strong acids ‘dissociate’ more in water so have a higher pH (as more H+ ions) Strong/Weak Acids

15. Common Strong Acids

16. Common Weak Acids

17.  Strong Bases ‘dissociate’ more in water so have a higher OH- ions.  These reduce the H+ ions present so have higher pH Strong/Weak Bases

18. Equations for Bases Strong Bases Weak Bases

19.  Titration: Determining the unknown concentration of a solution.  A type of titration is an acid/base titration. Calculations and Titrations

20.  We can perform an experiment where we add a base of known CONCENTRATION to a known VOLUME of acid.  Until all the acid has been neutralised (pH 7)  If we now know the volume of base added we can calculate the concentration of the acid.

21.  E.g We have added 10ml of 0.1M NaOH to 10ml HCl.  Calculate the concentration of acid.  Step 1: Write the BALANCED Formula.  Step 2: Calculate the number of moles of based added.  Step 3 Determine the AMOUNT of acid present in MOLES.  Step 4 Calculate the concentration of acid. Steps

22.  NaOH + HCl  NaCl + H 2 O Step 1 Notice it takes 1 mole of base to react with 1 mole of acid. We have added 10ml of 0.1M NaOH to 10ml HCl. Calculate the concentration of acid.

23.  We need to calculate the amount of sodium hydroxide added (in moles). Remember, in quantitative chemistry we always need to work in moles.  C = n / V  0.1 = n / 0.01 dm 3  n = 0.001 moles Step 2 We have added 10ml of 0.1M NaOH to 10ml HCl. Calculate the concentration of acid.

24.  If we used 0.001 moles of base with a 1:1 mole ratio, the amount of acid present is 0.001 moles. Step 3 We have added 10ml of 0.1M NaOH to 10ml HCl. Calculate the concentration of acid.

25.  Using our quantitative formula again. Remember, we use this formula whenever we are using solutions.  C = n / V  C = 0.001 / 0.01 dm 3  C = 0.1 mol dm -3 Step 4 We have added 10ml of 0.1M NaOH to 10ml HCl. Calculate the concentration of acid.