So 11, But let's just leave it like this. And then, let's just think about if we wait another years, so three times So you might notice a little bit of a pattern here. This is one half-life has gone by, two half-lifes, we have an exponent of two, three half-lifes, we multiply by three. So what's going to be a general way to express M of t? Well, M of t is going to be our initial value, , times, and you might already be identifying this as an exponential function, we're going to multiply times this number, which we could call our common ratio, as many half-lifes has passed by.
So how do we know how many half-lives have passed by? Well, we could take t, and we could divide it by the half-life. And try to test this out. When t is equal to , this exponent is going to be one, which we want it to be.
Understanding the radioactivity and half-life of a sample is important for calculating the correct dose for a patient and determining the levels and duration of radioactive emission from a patient after treatment is received. Frequently, dosages for radioactive isotopes are given the activity in volume. This relationship can be used to calculate the volume needed for a particular dose.
The first part of the problem is to find the dose given to the patient. We are given the volume and the concentration in units of radioactivity over volume. Now, we need to find the activity after After one half-life 8. After two half-lives total of After three half-lives total of Therefore, after Allison Soult , Ph.
Department of Chemistry, University of Kentucky. Learning Outcomes Define half-life as it relates to radioactive nuclides and solve half-life problems. Describe the general process by which radioactive dating is used to determine the age of various objects. Calculate the time for a sample to decay. Complete dosage calculations based on nuclide activity.
Clock-wise from the upper left: Deriving Moles from Grams for an Element According to nutritional guidelines from the US Department of Agriculture, the estimated average requirement for dietary potassium is 4.
What is the estimated average requirement of potassium in moles? Solution The mass of K is provided, and the corresponding amount of K in moles is requested. Referring to the periodic table, the atomic mass of K is The given mass of K 4. Deriving Grams from Moles for an Element A liter of air contains 9. What is the mass of Ar in a liter of air? Solution The molar amount of Ar is provided and must be used to derive the corresponding mass in grams.
Since the amount of Ar is less than 1 mole, the mass will be less than the mass of 1 mole of Ar, approximately 40 g. How many copper atoms are in 5. Deriving Moles from Grams for a Compound Our bodies synthesize protein from amino acids. One of these amino acids is glycine, which has the molecular formula C 2 H 5 O 2 N. How many moles of glycine molecules are contained in Solution Derive the number of moles of a compound from its mass following the same procedure used for an element in Example 3.
The recommended daily dietary allowance of vitamin C for children aged 4—8 years is 1. What is the mass of this allowance in grams? Solution As for elements, the mass of a compound can be derived from its molar amount as shown: The molar mass for this compound is computed to be Performing the calculation yields: 1. Deriving the Number of Atoms and Molecules from the Mass of a Compound A packet of an artificial sweetener contains Solution The number of molecules in a given mass of compound is computed by first deriving the number of moles, as demonstrated in Example 3.
Counting Neurotransmitter Molecules in the Brain The brain is the control center of the central nervous system Figure 3. Footnotes 1 Omiatek, Donna M. Andrews, Michael L. Heien, and Andrew G. Previous Next. Order a print copy As an Amazon Associate we earn from qualifying purchases. We recommend using a citation tool such as this one.
Use this page to learn how to convert between grams LiF and mole. Type in your own numbers in the form to convert the units! You can do the reverse unit conversion from moles LiF to grams , or enter other units to convert below:. In chemistry, the formula weight is a quantity computed by multiplying the atomic weight in atomic mass units of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all of these products together.
When calculating molecular weight of a chemical compound, it tells us how many grams are in one mole of that substance. The formula weight is simply the weight in atomic mass units of all the atoms in a given formula. A common request on this site is to convert grams to moles.
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