MAKING THE SOLUTION YOU WANT what do you do if the solution does not have the concentration you want you may not want to work with concentrated acid in the lab a very common task is to DILUTE solutions to the concentration they need DILUTION CALCULATIONS if the number of moles of solute stays the same regardless of amount of solvent added we can calculate the molarity of a solution based on the following equation M initial x V initital M final x V final Ex if you want 1L of M HCl starting from 12 M HCl 12M x V initial 1M x 1L V initial 1M x 1L 12M 0 083L 83mL Moles of solute constant Molarity x Volume of solution L SOLUTION STOICHIOMETRY remember that chemical stoichiometry calculations ALWAYS depend on mole ratios we must convert volumes to moles using molarity before we can do math on chemical reaction equations note that we can always convert between mass and volume using densities Chp 1 10 we can also convert mass to moles STEPS 1 use molarity as a conversion factor 2 use coefficients in the balanced equation to find mole ratios 3 use molarity as a conversion factor Ex how many mL of 1 0M NaOH are needed for the reaction with 10mL of 6 0M HCl HINT one of the products is NaCl HCl NaOH NaCl H2O 10mL x 1L 1000mL x 6mol HCl 1L 0 06mol HCl 0 06mol HCl x 1mol NaOH 1mol HCl 0 06mol NaOH 0 06mol NaOH x 1L 1mol NaOH x 1000mL 1L 60mL NaOH TITRATIONS titration refers to a procedure for determining the concentration of a solution by allowing a measured volume of the solution to react with a second solution of another substance the standard solution whose concentration is known sometimes concentrations may not be exactly known concentrations could change due to evaporation of solvent IMPORTANT we must be able to detect the point of completion for the reaction CARRYING OUT TITRATIONS the last reaction s that we looked at were an example of a specific type titration reaction Acid Base neutralization reaction Acid Base neutralizations always produce water and salt for titration a carefully measured volume of the unknown solution is put in a flask and measured using a buret TITRATIONS WATCH STOICHIOMETRY Ex How many mL of 1 0 M HCl are needed to neutralize 50mL of 1 0M Ba OH 2 2HCl Ba OH 2 BaCl2 H2O 50mL x 1L 1000mL x 1mol Ba OH 2 1L 0 05mol Ba OH 2 0 05mol Ba OH 2 x 2mol HCl 1mol Ba OH 2 0 1mol HCl 0 1mol HCl x 1L 1mol HCl x 1000mL 1L 100mL HCl DETERMINING COMPOSITION OF SUBSTANCES so far all substances we have discussed has a known formula the book or your teacher gave it to you How were they determined How can he formula for a completely new compound thing research be found we need to know the elements that are present and how much of each is present usually done by determining percent composition PERCENT COMPOSITION AND EMPIRICAL FORMULAS PERCENT COMPOSITION expressed by identifying the elements present and giving the mass percent of each EMPIRICAL FORMULA tells the smallest whole number ratios of the atoms in the compound MOLECULAR FORMULA tells the actual numbers of atoms in a compound It can be either the empirical formula or a multiple of it Multiple Molecular mass Empirical formula mass Ex a colorless liquid has a composition of 84 1 carbon sand 15 9 hydrogen by mass Determine the empirical formula Also assuming the molar mass of this compound in 114 2 g mol determine the molecular formula of this compound Mass percents Moles Mole ratios Subscripts Assume 100g of the substance Moles of Carbon 84 1g C x 1mol C 12 0g C 7 01mol C Moles of Hydrogen 15 9g H x 1mol H 1 01g H 15 9mol H Empirical Formula C7 01H15 9 need smallest value C1H2 27 multiply by four to get whole numbers C4H9 Molecular Formula Multiple 114 2 57 0 2 multiple empirical formula by multiple C4H9 x 2 C8H18