Monday, October 1 •  Lecture 4 (Last Week) –  Wri9ng Conversion Factors (1.8) –  Problem Solving (1.9) •  Lecture 5 (Today) –  GoPost Discussion Board –  LD50 Values –  Density (1.10) –  CHEM 120 Lab Info –  CHEM 120 Experiment #1 –  Naviga9on Inside ALEKS LD50 Values
•  One measure of toxicity is the LD50 or 50% lethal dose, which is
the concentration of the substance that causes death in 50% of
the test animals.
•  A dose is typically measured in ppm (mg/kg) of body mass or
ppb (µg/kg).
High LD50: low toxicity foods consumed for recrea9on or medicinal benefits Low LD50: very toxic! pes9cides © 2013 Pearson Educa9on, Inc. amatoxins (found
Amanita
mushrooms)
Chapterin
1, Section
8
0.1
3
Density Comparisons The density of a collec0on of ma2er depends on its chemical composi0on and its phase (solid, liquid, or gas). Density
Density
§  compares the mass of an object to its volume.
§  is the mass of a substance divided by its volume.
§  are measured in g/L for gases.
§  are measured in g/cm3 or g/mL for solids and liquids.
Density expression:
Densities of Common Substances
Using Density as a Conversion Factor 1.  A block has a volume of 25.3 cm3. Its mass is 21.7 g. What is the density of the block? 0.858 g/cm3 d = m V = 21.7 g 25.3 cm3 = 0.858 g/cm33 2.  A cube of magnesium (Mg) is needed that has the mass 60.5 g. What must be the length of the cube’s edge in cm? The density of Mg is 1.74 g/cm3. 3.26 cm L L d = m V = 60.5 g V L V = L3 V1/3 = L V = = 1.74 g/cm33 m d = 60.5 g 1.74 g/cm3 (30.77 cm3)1/3 = L = 3.26 cm3 = 30.77 cm33 Density: The volume of a rock weighing 1.705 kg is 334.5 mL. What is the density of the rock? a)
b)
c)
d)
5.097 × 10–3 g/mL
5.097 g/mL
0.1962 g/mL
196.2 g/mL
Measuring Density
1.  Measure the mass of the solid
2.  Measure its volume by
a.  measuring its dimensions and
calculating its volume
b.  submerging it in water to
determine its volume.
3.  Calculate the Density
density = © 2013 Pearson Educa9on, Inc. Chapter 1, Section 8
9
Measuring Density of Solids
Volume displacement is
the volume of a solid
45.0 mL calculated from the volume
35.5 mL of water displaced when it
is submerged.
•  This technique is used to measure the volume of irregularly shaped solids, like lumps of metal © 2013 Pearson Educa9on, Inc. Chapter 1, Section 8
10
CHEM 120 Lab Policies •  Goggles, labcoat, and appropriate clothing are mandatory •  Prelabs are collected at the beginning of the lab period •  Use lockers in Bagley for backpacks, etc. •  If you are more than 10 minutes late you cannot par9cipate in the lab o  Your TA explains important parts of the lab, including safety at the beginning of the period •  Postlab reports are due at the beginning of the next lab period CHEM 120 Lab Agendance Policies Learning Check
What is the density (g/cm3) of 48.0 g of a metal if the level of
water in a graduated cylinder rises from 25.0 mL to 33.0 mL
after the metal is added?
25.0 mL A.  0.17 g/cm3 B.  0.167 g/cm3 C.  1.5 g/cm3
D.  1.45 g/cm3 E.  6.0 g/cm3 F.  6.00 g/cm3 G.  I don’t know 33.0 mL 48.0 g object Step 1: measure the mass (already complete) Step 2: Calculate the change in volume 33.0 mL -­‐ 25.0 mL 8.0 mL Step 3: Calculate the density d = m V = 48.0 g 8.0 mL = 6 g/mL = 6.0 g/cm33 Densi9es of Solids vs. Liquids solid liquid H2O solid (ice) is less dense than liquid (water) liquid solid paraffin wax (and most substances) solid is more dense than liquid Density: how much mass is contained in a given volume? For solids and liquids, the volume of a sample is directly propor9onal to the mass of the sample. (For gases the situa0on is a li2le more complicated). We can define a propor9onality constant called “density” and write a expression for this rela9onship... m = d * v Fig. 3-­‐9, p. 81 The ALEKS Pie: My View class average total # of topics in course boundaries of the current Objec9ve The ALEKS Pie: Your View If your course mastery is Arrows show you which areas have unfinished topics in the current objec9ve Shading indicates por9ons that you have finished The ALEKS Pie: Your View •  When you mouse over an arrow it shows a list of the topics in the current objec9ve that you have not completed The ALEKS Gradebook The Gradebook bugon Objec9ve Deadline •  Your progress through the Objec9ve •  This number will “lock in” amer the Objec9ve deadline •  You don’t really want to get ahead on ALEKS assignments •  try to stay in sync with the Objec9ve deadlines and the lecture