So here it says, if it takes 25.13 ml of 0.320 molar barium hydroxide to titrate 31 ml of a solution containing hydrochloric acid, what is the molar concentration of hydrochloric acid? Alright. So to solve this, we're going to do the following steps. First, we're going to convert the given quantity into moles of given. Our given quantity is this part here. It's volume of molarity. Think of this as a complete set. "Of" means multiply, and remember that moles equals liters times molarity. So, if I change these milliliters into liters and multiply them by the molarity, that'll give me the moles of barium hydroxide. Alright. So what I'm going to do first is I'm going to have 0.02513 liters. I converted it into liters already. Remember that the molarity means moles over liters, so that's 0.320 moles of barium hydroxide per 1 liter. Liters cancel out, and what I've just done is found the moles of given, the moles of barium hydroxide.

Now step 2 says to do a mole to mole comparison to convert moles of given into moles of unknown. Alright. So we look at the balanced equation. We put moles of barium hydroxide here on the bottom so it can cancel out, and moles of hydrochloric acid here on top. According to my balanced equation, for every one mole of barium hydroxide, we have 2 moles of hydrochloric acid. So these moles cancel out. Now at this point, this will give me the moles of hydrochloric acid, which are 0.0160832 moles.

Next, it says, if necessary, convert the moles of unknown into the desired units. We have to go a step further; we have to find molarity. So, if the molarity is required, then divide the moles of unknown by its liters. So I just found the moles of my unknown, but that's not my molarity, that's not my molar concentration. I'm going to take those moles that I just found and then divide it by its liters. HCl has 31 ml's, which when you convert to liters is 0.031 liters. Here, that'll give me my molarity as 0.519 molar HCl. So this would be my final answer for this particular question.