lab reports - second experiment, Lab Reports of Chemistry

Download lab reports - second experiment and more Lab Reports Chemistry in PDF only on Docsity! 2.1 Experiment 2 Intensive Properties: Density Introduction Intensive properties are characteristics of a substance which enable us to describe that substance and to distinguish it from any other substance. Extensive properties, on the other hand, are properties which depend on the amount of the substance present. Properties may be classified as physical or chemical. Physical properties include such properties as color, melting point, boiling point, electrical conductivity, density, etc. Chemical properties include a description of what a substance is composed of (its chemical composition) and how the substance can be converted into some other substance (chemical reactivity). The density (d) of a substance is defined as its mass (m) divided by its volume (V). (2.1) Since the SI units for mass and volume are the kg and m3, respectively, the SI units for density are kg @ m!3. For most common purposes, these are inconvenient units with which to work, so we often express the density of liquids or solids in terms of g @ cm!3 or g @ mL!1. Mass and volume are both extensive properties. The ratio of the mass of a substance to its volume (its density), however, is independent of the amount of substance present and is therefore classified as an intensive property. In determining the density of a substance, two quantities must be measured, the mass and the corresponding volume. Mass is easily measured using a balance. Similarly, the volume of a regularly shaped object (e.g. a spherical or rectangular object) is also easily determined by measuring the geometric characteristics (diameter, length, width, etc.) of the object. However, it is frequently the case that solid samples we encounter do not have a regular shape. For an irregularly shaped solid, the volume can be determined in an indirect manner. If a solid is placed in a liquid in which it does not dissolve and which has a smaller density, the solid will sink and displace a volume of the liquid equal to its own volume. If the liquid is contained in a graduated container, the volume of the liquid displaced and hence the volume of the solid itself can be easily measured. In this experiment, you will determine the density of a known metal sample by two different methods. You will then determine the percent error for each method. 2.2 Experimental Procedure Although the balances are routinely calibrated, there may be slight differences between any two balances. Using different balances in a single procedure, therefore, is a potential source of error. It is critical, therefore, that you use the same balance for all of your weighings in a given procedure. I. Density by Direct Measurement Obtain a small, clean, dry square bottle and cap. If the bottle is not dry, add a little acetone, cap the bottle and shake it. Pour the acetone into the waste bottle provided and allow the residual acetone in the bottle to evaporate. Weigh the bottle along with its cap and record the mass. To determine the volume of the bottle, add deionized water to bottle until it is completely filled. Carefully cap the bottle and tighten the cap so as not to introduce any air bubbles. Once the bottle is capped snuggly, invert it and carefully check for air bubbles. If there are any air bubbles present, remove the cap, add more water and replace the cap. Dry the outside of the bottle and weigh it again. Determine the mass of the water in the bottle by difference. Remove the cap and measure the temperature of the water to the nearest 0.1°C. Look up the density of water at this temperature in Table 2 and use the mass and density to calculate the volume of water. Since the water completely fills the bottle, its volume corresponds to the volume of the bottle. Dry the bottle with acetone as before and add your metal sample to the bottle until it is at least half full or until you’ve added all your metal. Weigh the bottle, cap and metal and determine the mass of the metal in the bottle. Add water to the bottle containing the metal until the bottle is completely filled. Replace the cap and ensure that there are no air bubbles present by carefully rolling the metal sample in the bottle and inverting it. When the bottle is free of air bubbles, dry the outside of the bottle and weigh it again to obtain the mass of water in the bottle. Remove the cap and measure the temperature of the water to the nearest 0.1°C. Look up the density of water at this temperature and use the mass and density to calculate the volume of water now in the bottle. The volume of the metal is the difference between the volume of the bottle itself and the volume of the water now in the bottle. Calculate the density of the metal from its mass and volume. II. Graphical Determination of Density Dry the metal used in part I. Place a #2 rubber stopper1 in the bottom of a 100 mL graduated cylinder. Add deionized water to near the 50 mL mark. Record the volume to the nearest 0.1 mL in the data table. Dry the exterior of the graduated cylinder and weigh it. Record the mass. Divide your metal sample into 5 roughly equal portions. Add the first group of metal pieces to the graduated cylinder being careful to avoid splashing the water. Record the new volume and mass. Repeat this procedure until you have added all 5 portions of your metal sample. It is important that the metal not break the surface of the water. Plot the mass of the graduated cylinder and its contents as a function of the total volume of the water and metal (points only). How does the slope of this line relate to the density of the metal? Perform a linear regression on your data and plot the calculated line on the same graph. Display the equation of the best fit straight line on the plot. Obtain the slope of the calculated line. 1The rubber stopper is placed in the graduated cylinder to prevent accidental breakage when the metal pieces are added. 2.5 Name ______________________________ Lab Section _____________ Report Sheet: Intensive Properties: Density Data Unknown Number ______________ Identity of Metal (if provided) ______________ Mass of dry empty bottle and cap ____________ g Mass of bottle, water and cap ____________ g Temperature of water ____________ °C Density of water at T ____________ g/mL Mass of bottle and metal ____________ g Mass of bottle, metal and water ____________ g Temperature of water ____________ °C Density of water at T ____________ g/mL Sample Total volume of water and metal (mL) Mass of cylinder and contents (g) Total volume of metal (mL) Total mass of metal (g) Calculated density (g/mL) 0 0.0 0.000 1 2 3 4 5 Attach a copy of the graph 2.6 Calculations Determining the Volume of the Bottle Mass of water (Show work.) ____________ g Volume of water = volume of bottle (Show work.) ____________ mL Density of Metal by Direct Measurement Mass of metal (Show work.) ____________ g Mass of water (Show work.) ____________ g Volume of water (Show work.) ____________ mL Volume of metal (Show work.) ____________ mL Density of metal (Show work.) ____________ g/mL Accepted density of metal (if given) ____________ g/mL % Error in Direct Determination (Show work.) ____________ % 2.7 Graphical Determination of Density (Attach a copy of the graph) Density of metal from the plots ____________ g/mL Accepted density of metal (if given) ____________ g/mL % Error in Graphical Determination (Show work.) ____________ % Average Density from individual determinations (Show work.) ____________ g/mL % Error (Show work.) ____________ %