Video Transcript
An aqueous solution of NaOH that contains five milliliters of 0.5 molar is needed to complete the neutralization of 2.5-molar HBr. Determine the final reading in milliliters if the initial reading of the buret was 3.5 milliliters to the nearest one decimal place.
As NaOH and HBr were reacted with one another, we can start by writing a balanced chemical equation to represent this reaction. The reaction of sodium hydroxide, a base, with hydrobromic acid produces sodium bromide, a salt, and water.
Neutralization of an acid with a base is often carried out via a titration experiment. We should therefore recall the key equation for solving titration problems: 𝑛 equals 𝑐𝑣, where 𝑛 represents the amount in moles, 𝑐 is the concentration in moles per liter, and 𝑣 is the volume in liters. We can make a table to match the values given in the question with the variables of our key equation. We will also record the molar ratio of the acid and base.
This neutralization reaction required five milliliters of a 0.5-molar NaOH solution. We can add this concentration to the appropriate box in our table, recognizing that molar and moles per liter are equivalent units. The volume is given in milliliters but must be converted into liters in order for the liters in the concentration unit to cancel when solving. Recognize that 1000 milliliters are equivalent to one liter. We can then multiply the five milliliters by one liter over 1000 milliliters. This gives us a volume of 0.005 liters.
The NaOH solution was used to neutralize a solution of 2.5-molar HBr. The question asks us to determine the final reading of the buret. In order to do so, we will need to calculate the volume of HBr that was used during the experiment.
Now that the given values have been filled into the table, we are ready to solve the problem. We can substitute our sodium hydroxide concentration and volume into the key equation to determine the number of moles of sodium hydroxide to be 0.0025 moles. Now that we know the number of moles of base used, we can determine the number of moles of acid used in the experiment. Looking at the balanced chemical equation, we can see that the molar ratio of sodium hydroxide to hydrobromic acid is one to one. Therefore, if 0.0025 moles of sodium hydroxide are necessary for complete neutralization, then 0.0025 moles of hydrobromic acid are also necessary.
Next, we can rearrange our key equation to solve for the volume of hydrobromic acid. We can substitute our HBr amount and concentration to determine the volume of HBr to be 0.001 liters. However, the question asks us to determine the final reading in milliliters. We must therefore convert our answer into milliliters. We can accomplish this by multiplying our answer by 1000 milliliters over one liter. This gives us a volume of one milliliter. This represents the volume of hydrobromic acid used in the reaction. But we need to determine the final reading of the buret.
A buret is a graduated piece of glassware used to deliver an accurate volume of liquid. The graduations on a buret begin with a zero at the top and increase in value as you move down the buret. In this experiment, the buret was filled so that the initial reading was 3.5 milliliters. In order to complete the neutralization reaction, one milliliter of HBr was released from the buret. As the graduations on a buret increase in value as you move down, releasing one milliliter of liquid will result in a final reading of 4.5 milliliters.
