MODULE 2 12 WORKSHEET CONCEPTS OF ACIDS Syllabus reference 9.3.4 1 To check your understanding, fill in each of the following blanks with a word or phrase. a Compounds can be classified as acids or bases according to a number of different theories. sour Originally an acid was a substance with a __________ taste and which reacted with certain hydrogen metals to produce ________________ gas. Antoine Lavoisier attempted to define acids on the chemical basis of their ______________ composition. He proposed that acids were substances which oxygen contained ______________. This theory was soon disproved because although many non-metallic acids metallic oxides formed bases when dissolved in water. oxides formed __________ in water, ___________ b Davy hydrogen An English chemist, Sir Humphrey _________, suggested that acids contained ____________ salts rather than oxygen and that acids reacted with metals to form ____________. Bases were water defined as substances that reacted with acids to form salts and _______________. c Svante Arrhenius developed a definition to explain the properties of acids. He proposed that hydrogen an acid was a substance which produced ______________ ions in aqueous solution. If the acid completely but if it was weak it ionised only ________________. slightly was strong it ionised _____________ hydroxide Arrhenius defined a base as a substance which produced ________________ ions in aqueous solution. One problem with the Arrhenius definition is that it can only be applied to aqueous _______________ solutions and does not allow for different solvents. d A more general definition was developed by the two chemists, Lowry and Brönsted. According to the Brönsted–Lowry definition, an acid is a substance that in solution donates a proton acceptor _______________. A Brönsted–Lowry base is a proton ________________. According to this donates conjugate theory, the acid ______________ a proton to form its ________________ base. Similarly, a proton acid base accepts a _______________ to form its conjugate __________. A substance which can act amphiprotic as a proton donor and as a proton acceptor is called __________________. Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 12 2 Write equations for the following showing the formation of the hydronium ion, H3O, in aqueous solution. a HNO3 HNO3 H2O → H3O NO3 b HF HF H2O → H3O F c H2CO3 H2CO3 H2O d HSO4 HSO4 H2O 3 4 H3O HCO3 H3O SO42 Write equations for the following showing their basic nature in aqueous solution. a NaOH NaOH → Na OH b HS HS H2O → H2S OH c NH3 NH3 H2O → NH4 OH d KHCO3 KHCO3 H2O → K H2CO3 OH Give the conjugate bases of the following acids. a NH4 NH3 b HCN CN Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 12 c H3O H2O d HOBr OBr 5 Give the conjugate acids of the following bases. a Cl HCl b CN HCN 6 c HPO42 H2PO4 d N2H4 N2H5 For each of the following reactions, identify the acid on the reactant side of the equation and its conjugate base. a HCOOH CO32 HCOO HCO3 � �������������� ����� ������� � �� ���� ���������� � � ����������� � ����� � � � ���� ���� � � � � ������ ���������� � HCN ����� b�� CN �� H�2� O�2����������� �� ���� � HO2 � � � ���� � ���� ��������� � � � ���� ���� �� ���� �� � � � ���� ���� ����� � �� ��������� � � �� ���� � � �� � �� ����� ������ � �� �c � � � �� ����� � ����HNO ���� � S2 ���� ���� ���� ���� � � � HS NO 3 � � � ���� �� ������ � 2 ����� ���������� � ���� Copyright © 2007 McGraw-Hill Australia ���� CONQUERINGCHEMISTRY HSC MODULE 2 WS 12 7 For each of the following reactions, identify the base in the reactant side of the equation and its conjugate acid. a HSO3 HS H2S SO32 � � � � ���� ����� � � � ���� ���� ����� � ���� ������������ ���� �� ��������� � ���� � � �� � �� CO 2 ��� � �� ������ ������ b�� CH HCO CH ���3��O����� ������ ������� � � 3 3OH 3 � � � � � ���� � ���� ���� ���� �� � ������� � ��� ����������� � � � � � �� �� ���� ���� �� ������ � �� ��� ������� � ��� ��� �� ������ � �������� � � � � �� �� �c �� ���� 2 ����� � 3 ���������� � ���� ���� ���� � �PO � HPO NH NH 4 4 3 4 � � ������ ��� ������ � ���� �� ����������� � ���� ���� 8 Tartaric acid is diprotic while citric acid is triprotic.Write equations for the stepwise dissociation of the acids given. All acids here are weak so use appropriate arrows. a citric acid (H3C6H5O7) H3C6H5O7 b H2C6H5O7 H HC6H5O72 HC6H5O72 H C6H5O73 tartaric acid (H2C4H4O6) H2C4H4O6 H HC4H4O6 HC4H4O6 c H C4H4O62 HOCl HOCl 9 H H2C6H5O7 H OCl HCO3 is amphiprotic. Write one equation to show it acting as an acid and another to show it acting as a base. Base HCO3 H2O H2CO3 OH Acid HCO3 H2O H3O CO32 Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 12 10 Write the formula of each of the following salts and classify it as acidic, basic or neutral. a potassium acetate KCH3COOK basic b sodium nitrate NaNO3 c potassium cyanide KCN d neutral ammonium bromide NH4Br f basic sodium sulfate Na2SO4 e neutral acidic potassium carbonate K2CO3 basic Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 12
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