The volume of an adult's stomach ranges from about 50 mL when empty to 1 L when full. If the stomach volume is 400 mL and its contents have a pH of 2, how many moles of H+ does the stomach contain? Assuming that all the H+ comes from HCl, how many grams of sodium hydrogen carbonate will totally neutralize the stomach acid?

Video transcript

Hello everyone. So in this video we're solving for the moles of H plus ions in the solution as well as the grams of sodium hydroxide that is required to completely neutralize the solution. So first we are given the ph value and that is of value 2.850. What we can do with this information is to calculate for the concentration of H plus ions. If you recall that the equation for this is 10 to the power of negative P. H. So just plugging that in, We have 10 to the negative 2.850. Putting that value into my calculator, I will get that the concentration of H plus ions is equal to 0. molars. And just to refresh that the concentration unit is moles per leader. So starting off with my dimensional analysis of the volume of the solution were given to us 355 ml of solution. I want to go ahead and first convert my military unit into leaders. So of course we have millions on bottom and leaders on top. So for every one leader we get 1000 ml and we can see that the male leaders unit will cancel. Next. I will go ahead and use the modularity of the H plus ions To go ahead and cancel our volume. So we have 0. moles on top. And one later on the bottom again we can see that the volume units of leaders will go ahead and cancel. So once we put all of these values into the calculator, we will get the value of the moles of H plus ions. So that's 5.1 times 10 to the negative four moles of R H plus ions. So going ahead to scroll down a little bit to give us more space, we will first need to highlight this because this is one of our answers. Next is to see how many, how much sodium hydroxide we need to go ahead and completely neutralize this um solution. So first thing I want to go ahead and actually do is write out the chemical equation of our H plus ions reacting with our sodium hydroxide. So if those two are reacting, those are going to be our starting re agents. So we have again the H plus ions that is that's going to go ahead and react with our sodium hydroxide. Again, that is, we can see here that this is going to be a single displacement reaction. So what we will get is R. N. A plus carry on and H 20. Which is a liquid of course. So starting off my dimensional analysis in this case, we're going to go ahead and use the moles of our H plus, which is what we saw for in the first part. So we have 5.1 times 10 to the negative four moles of our H plus ions. What we're gonna do here is use store geometry and that's why it's very important to write out our chemical equation first. We want to go ahead and solve for the moles of N. A. O. H. So we can see here that it is a 1 to 1 ratio. So we have one moles of our H plus K ions on the bottom and one mole of sodium hydroxide on top. You can see here that the moles of H plus will cancel out beautifully. Next step here we have the moles of any O. H. But we want the mass of any O. H. How you can do this is by using the um molar mass. Some bottom we have again one mole of N. A. O. H. And for every one mole of sodium hydroxide we get 40.0 g of sodium hydroxide. So again you can see that the molds of Noh will cancel putting all these american values into my calculator. I'll get the value of 0.201 and units being grams of sodium hydroxide. So this is how much sodium hydroxide it will take to completely neutralize my solution. And this is going to be the moles of H plus in the solution. Thank you all so much for watching