Bromine has two naturally occurring isotopes; 79Br (mass of 78.918) and 81Br (mass of 80.916). If the atomic weight of bromine is 79.904, predict the mass spectrum of a sample of bromine atoms. (LO 2.17) (a)

(b)

(c)

(d)

Video transcript

Hello everyone today. We have the following problem. The element silver has to naturally occurring isotopes. The isotope of silver one oh seven has a massive one oh 6.905. And the isotope silver 109 has a massive 108.905. Which of the following is the mass spectrum of a sample of silver atoms, given the atomic weight of silver is one oh 7.8 68. So first thing we wanna do is you want to determine the atomic mass equation, which is going to be equal to our fraction times The mass of our isotope one plus the fraction Times are a mass of Isotope two. So we're gonna do this for each one and determine which one matches up. So for a We have silver, 107 and 109. So the fraction for our 107 or silver 107. It's going to be equal to 48. As it's presented here. We have 48/48 plus 100. That's going to give us 0.3-4. And we'll find the fraction for our 109, silver as well, which will be 100 Over plus 100, which gives us .676. And so we're going to solve for the atomic mass unit. Is am We're just going to be .3-4 times the mass of that one oh 6.905 plus hour 0.676 times the mass of that silver isotope, that silver 109, which is one of 8.905. And that gives us an atomic mass of 257. So this is not going to be our answer so we can cross our answer choice A for answer choice B. We're going to follow the same pattern. We're going to find the fraction for our isotope Which is going to be over 100 that mass plus the mass of 19 which is about 93. That gives us .518. And then the fraction of our 109 silver isotope is going to be that 93 over 100 plus 93 giving us 0.482. As before we're gonna solve for our atomic mass. We're just going to be taking these fractions and multiplying them by their atomic weights. So we're gonna have .518 Times that 106.905 Plus our .42 times Our .905. And this is going to give us a mass of 107. which is right on the dot as our answer choice was in the question stem. And so this is actually gonna make anti choice, be our correct answer. And so we don't even have to go through answer choices C. Or D. Overall I hope this helped until next time