The AP Chemistry Summer assignment is meant to help prepare you for the first few weeks of class

Transcription

1 The AP Chemistry Summer assignment is meant to help prepare you for the first few weeks of class Part 1. Review the mole concept and how it s used. This includes mass (grams) to moles, moles-to-mass calculations, as well as percentage composition and mole ratios from balanced chemical equations. Part 2. Be familiar with the rules governing significant figures. Practice mental math (non-calculator) calculations using the following website: There will be a quiz on the first day of school. A sample quiz is at the end of this document. If you have any questions please Mr. Miehl at Michael_J_Miehl@mcpsmd.org. Sample Quiz Name, formula of Molar mass of Number of moles in 100 g of substance w/ correct sig figs Percentage composition of each element in : hydrochloric acid, HCl phosphoric acid, H3PO4 hydrofluoric acid, HF Please answer the following. Try to do so without the use of a calculator. 1. What is the answer to the following : 2.0 x 10-4 x 2.0 x How many sig figs does the following number have? ? 3. Circle the best answer to the following: log =? ( ) 3.5 = 5. In the chemical equation 2H2 + O2 2H2O this is how many moles of water can be formed from 5.0 moles of oxygen with excess hydrogen.

2 Sample Quiz answers Note: explanations are in gray Name, formula of Molar mass of Number of moles in 100 g of substance w/ correct sig figs Percentage composition of each element in : hydrochloric acid, HCl = 36.5 g/mol 100 g / 36.5 g/mol = 2.73 mol 1.0/36.5 x 100 = 2.7% H 35.45/36.5 x 100=97.1% Cl phosphoric acid, H3PO4 1 x x 4 = 98 g/mol 100 g / 98 g/mol = 1.0 mol 3/98 x 100 = 3.1 % H 31/98 x 100 = 31 % P 64/98 x 100 = 65 % O hydrofluoric acid, HF = 20 g/mol 100 g / 20g/mol = 5.0 mol 1 / 20 x 100 = 5% H 19/20 x 100 = 95% F 1. What is the answer to the following : 2.0 x 10-4 x 2.0 x 10-2 = 2x2 = 4 and = -6 so 2.0 x How many sig figs does the following number have? ? = 3 The 3 zeros (in bold) in the front of the number are only decimal place holders. The significant figures are those underlined. 3. What is the answer to the following: log =? has only 2 significant figures (the 1 and the 3 are significant; the 2 zeros in front of those numbers are just decimal place holders and are NOT significant) so the answer to the log should also have 2 significant figures, i.e The 1 in this value is not significant. 4. ( ) 3.5 = = (Follow order of operations. When adding or subtracted, only look to the decimal places; your answer will have the same number of decimal places as the number you added/subtracted with the fewest decimal places.) Then you divide by 3.5 you get but since 3.5 only has 2 significant figures, your final answer will have only 2 significant figures ( rounded to 4.2). 5. In the chemical equation 2H2 + O2 2H2O this is how many moles of water can be formed from 5.0 moles of oxygen with excess hydrogen. Since there are only 2 reactants in this reaction, when hydrogen is in excess, this implies that oxygen is the limiting reactant, and all calculations are therefore based upon the oxygen s quantity: 5 moles O2 x 2 moles H2O/1 mole O2 = 10 moles of H2O are formed. The mole ration 2 moles H2O/1mole O2 is taken directly from the coefficients in the balanced chemical equations.

3 Uncertainty Uncertainty is present in all measurements and depends on the precision of the measuring device. Precision is not Accuracy o Precise is multiple similar values o Accurate close to the true/accepted value For this reason significant figures are used to record the certain digits and the first uncertain digits in a measurement. Rules for significant figures: o Nonzero integers- Nonzero integers always count as significant figures o Leading zeros are insignificant o Zeros in between nonzeros are significant o Zeros following significant figures after the decimal are significant Rules for significant figures in math operations: o Multiplication or division: Sig. figs = number of sig. figs in the least precise measurement o Addition or Subtraction: Has the same number of decimal places as the least precise measurement o Logarithms: The number of significant figures in the mantissa (decimal) of a value equals the number of significant figures to the right of the decimal in the logged value. Ex: -log (2.50) =.40 When taking antilogarithms, the resulting number should have as many significant figures as the mantissa in the logarithm (so the antilog of = 2.00, and antilog(0.30) = 2.0) Rules for Rounding o Carry all digits throughout the calculations and only round at the end o If the digit is less than 5, then the preceding number remains the same o If the digit is greater than 5, the preceding digit is increased by 1 Error Indeterminate (Random) Error result of uncontrollable conditions affective observer. Equal probability of being high or low. Reduced by taking multiple trials. Determinate (Systematic) Error result from faulty methods, technique or equipment. Definite in size and sign. Reduced by proper instrument calibration and refinement of the experiment s working equations. Percent Error - true value experimental value x 100 true value Mole concept review The formula weight of a equals the sum of the atomic weights (from the periodic table) of the atoms in its formula. If the formula is a molecular formula (i.e. for a covalent ) the formula weight is also called the molecular weight. Atomic weights and molecular weights can be used to determine the elemental composition of a A mole of any substance is Avogadro s number (6.02 x or 6 x for AP purposes) of formula units of that substance. The mass of a mole of atoms, molecules, or ions (the molar mass) equals the formula weight of that material expressed in grams. The mass of one molecule of H2O, for example, is 18 amu, so the mass of 1 mol of H2O is 18 g. That is, the molar mass of H2O is 18 g/mol. The empirical formula of any substance can be determined from its percent composition by calculating the relative number of moles of each atom in 100 g of the substance. The mole concept can be used to calculate the relative quantities of reactants and products involved in chemical reactions. The coefficients in a balanced equation give the relative numbers of moles of the reactants and products. The limiting reactant is completely consumed in a reaction. When it is used up, the reaction stops, thus limiting the quantities of products formed and determines their quantity.

4 Periodic Table, your friend in AP chemistry and beyond:

5 Hello Congratulations! You have selected to take AP chemistry next year. You will not be disappointed if you put forth a strong effort. Please see Mr. Miehl in room K-281 at your earliest convenience before June 14 for your required summer assignment. Hello Congratulations! You have selected to take AP chemistry next year. You will not be disappointed if you put forth a strong effort. Please see Mr. Miehl in room K-281 at your earliest convenience before June 14 for your required summer assignment.